ENH: multiindex formatting
closes #12423

```
In [1]: pd.options.display.width=80

In [2]: pd.options.display.max_seq_items=10

In [3]: pd.options.display.max_seq_items=100

In [4]:         mi = pd.MultiIndex.from_tuples([('A', 1), ('A', 2),
                                        ('B', 3), ('B', 4)])

In [5]: mi
Out[5]: 
MultiIndex(levels=[[u'A', u'B'],
                   [1, 2, 3, 4]],
           labels=[[0, 0, 1, 1],
                   [0, 1, 2, 3]])

In [6]:         mi = MultiIndex.from_product([list('abcdefg'),
                                      range(10),
                                      pd.date_range('20130101', periods=10)],
                                     names=['first', 'second', 'third'])

In [7]: mi
Out[7]: 
MultiIndex(levels=[[u'a', u'b', u'c', u'd', u'e', u'f', u'g'],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
                   ['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06', '2013-01-07', '2013-01-08', '2013-01-09', '2013-01-10']],
           labels=[[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    ...
                    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6],
                   [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2,
                    ...
                    7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4,
                    ...
                    5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]],
           names=[u'first', u'second', u'third'])

```

@TomAugspurger @jorisvandenbossche @sinhrks @shoyer @wesm 

hmm, I see a double comma already........
 could probably squeeze `name,dtype` in for each level I think.
 comments?
 Something like 

```
           labels=[[0, 0, 0, 0, 0, ... 6, 6, 6, 6, 6],
```

instead of 

```
           labels=[[0, 0, 0, 0, 0,
                    ...
                    6, 6, 6, 6, 6],
```

would maybe be clearer?

But, in any case, following `max_seq_items` is a good improvement
 In the example you pasted above (copied from there):

```
In [11]: mi
Out[11]: 
MultiIndex(levels=[[u'a', u'b', u'c', u'd'],
                   [0, 1, 2]],
           labels=[[0, 0, 0, 1, 1, 1, 2, 2,
                    2, 3, 3, 3],
                   [0, 1, 2, 0, 1, 2, 0, 1,
                    2, 0, 1, 2]],
           names=[u'first', u'second'])
```

Is there a reason the individual labels lists break of and do not fit on one line? It seems they should fit on one line?
 I think that last might be a bug. I have to twiddle the justification settings.
 so I think there is a bug in the current formatter that basically hard-codes 10 as the truncated width, here is a modification that uses 1/2 of the max_seq_items and bounds it between 10 and 50 (so it has some flex) (this is of course limited by the display_width as well)

```
In [9]: pd.options.display.max_seq_items=50

In [10]: Index(list(range(100)))
Out[10]: 
Int64Index([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
            ...
            75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99],
           dtype='int64', length=100)

In [3]: pd.options.display.max_seq_items=30

In [4]: Index(list(range(100)))
Out[4]: 
Int64Index([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            ...
            85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99], dtype='int64', length=100)

In [5]: pd.options.display.max_seq_items=20

In [6]: Index(list(range(100)))
Out[6]: 
Int64Index([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
            ...
            90, 91, 92, 93, 94, 95, 96, 97, 98, 99], dtype='int64', length=100)

In [7]: pd.options.display.max_seq_items=10

In [8]: Index(list(range(100)))
Out[8]: 
Int64Index([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
            ...
            90, 91, 92, 93, 94, 95, 96, 97, 98, 99], dtype='int64', length=100)
```
 so with the above change (and allowing labels & levels to have different max_seq_items), though still limited to (10,50) range

```
In [1]: pd.options.display.width=200

In [2]: pd.options.display.max_seq_items=50

In [3]: mi = MultiIndex.from_product([list('abcdefg'), range(10), pd.date_range('20130101',periods=10)],
                                     names=['first', 'second', 'third'])

In [4]: mi
Out[4]: 
MultiIndex(levels=[[u'a', u'b', u'c', u'd', u'e', u'f', u'g'],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
                   ['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06', '2013-01-07', '2013-01-08', '2013-01-09', '2013-01-10']],
           labels=[[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    ...
                    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6],
                   [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2,
                    ...
                    7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4,
                    ...
                    5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]],
           names=[u'first', u'second', u'third'])

In [5]: pd.options.display.max_seq_items=30

In [6]: mi
Out[6]: 
MultiIndex(levels=[[u'a', u'b', u'c', u'd', u'e', u'f', u'g'],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
                   ['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06', '2013-01-07', '2013-01-08', '2013-01-09',
                    '2013-01-10']],
           labels=[[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    ...
                    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6],
                   [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1,
                    ...
                    8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9],
                   [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4,
                    ...
                    5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]],
           names=[u'first', u'second', u'third'])
```
 One option where there are a lot of levels could be to display them like a `DataFrame`. Although that's a fair distance from where we are now
 ok updated a bit. The above is with the default options (though width is 80)
 @sinhrks 

if you have a chance. can you see if these changes look resonable for the truncation / formatting in categoricals

```
[Tue Apr 26 15:11:58 ~/pandas]$ nosetests  pandas/tests/indexes/test_multi.py pandas/tests/indexes/test_category.py pandas/tests/indexes/test_base.py 
..............................................................................................................................................................................................F................................................................................................................F............
======================================================================
FAIL: test_string_categorical_index_repr (pandas.tests.indexes.test_category.TestCategoricalIndex)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jreback/pandas/pandas/tests/indexes/test_category.py", line 638, in test_string_categorical_index_repr
    self.assertEqual(unicode(idx), expected)
AssertionError: u"CategoricalIndex([u'\u3042', u'\u3044\u3044', u'\u3046\u3046\u3046', u'\u3042' [truncated]... != u"CategoricalIndex([u'\u3042', u'\u3044\u3044', u'\u3046\u3046\u3046', u'\u3042' [truncated]...
Diff is 711 characters long. Set self.maxDiff to None to see it.

======================================================================
FAIL: test_string_index_repr (pandas.tests.indexes.test_base.TestIndex)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jreback/pandas/pandas/tests/indexes/test_base.py", line 1465, in test_string_index_repr
    self.assertEqual(coerce(idx), expected)
AssertionError: u"Index([u'a', u'bb', u'ccc', u'a', u'bb', u'ccc', u'a', u'bb', u'ccc', u'a',\n  [truncated]... != u"                Index([u'a', u'bb', u'ccc', u'a', u'bb', u'ccc', u'a', u'bb',  [truncated]...
Diff is 670 characters long. Set self.maxDiff to None to see it.

----------------------------------------------------------------------
Ran 316 tests in 5.779s

FAILED (failures=2)
```

couple of failing tests. I am not sure of the parameters that were used to initially generate these. I have hard coded in a context manager, but I am doing something wrong.
 closing, but maybe someone can pick this up.
 It would also depend a bit on what we do with https://github.com/pydata/pandas/issues/13480 (issue about changing the default multi-index repr)
