DOC Add more examples to Series.Resample docstring
Partial fix for https://github.com/pydata/pandas/issues/5023
flake8 doesn't do a very good job at checking code in the docstrings for PEP8 compliance, so I'm just eyeballing it at the moment and my PEP8 knowledge leaves something to be desired. Apologies if I missed something really obvious.

Will squash everything into one commit once I add an example of using a custom `how` method.
 @jorisvandenbossche @sinhrks 
this one is done and good to go from my side!
comments/corrections welcome, of course!
 Nice examples!
 Looks nice! No further comments from me. 
 @Winterflower Do you have some time to update? (it's only a very small comment)
 @jorisvandenbossche apologies for the delay! I will add the how='right' example tonight after work.
 Still need to fix line lengths.
 At the moment, the doctest for the string is failing because of the `custom_resampler` function defined in the docstring

```
Trying:
    def custom_resampler(array_like):
Expecting:
            return np.sum(array_like)+5
**********************************************************************
File "pandas/core/generic.py", line 3367, in generic.NDFrame.resample
Failed example:
    def custom_resampler(array_like):
Exception raised:
    Traceback (most recent call last):
      File "/home/winterflower/anaconda/lib/python2.7/doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest generic.NDFrame.resample[9]>", line 1
        def custom_resampler(array_like):
                                        ^
    SyntaxError: unexpected EOF while parsing
```

The solution, based on [this](http://stackoverflow.com/questions/13510698/python-how-can-i-define-a-class-in-a-doctest) is to include the ellipsis in the docstring. Will add that to make the doctests pass.

```
def custom_resampler(array_like):
...     return np.sum(array_like)+5
```
 This is good to go on my part! 
 @Winterflower gr8 thanks!

Further I think portions of your narrative my be a nice addition to the actual resample docs; add where appropriate
