Option_context Dictionary argument
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

Not a documentation sprint participant

Please include the output of the validation script below between the "```" ticks:

```
root@dfb9f788ea02:/pandas# scripts/validate_docstrings.py pandas.option_context

################################################################################
###################### Docstring (pandas.option_context)  ######################
################################################################################

Context manager to temporarily set options in the `with` statement context.

You need to invoke as ``option_context(pat, val, [(pat, val), ...])``.
You may also invoke using a dictionary of (pat, val) pairs:
``option_context(options={pat:val})``

Examples
--------

>>> with option_context('display.max_rows', 10, 'display.max_columns', 5):
        ...
Traceback (most recent call last):
  File "scripts/validate_docstrings.py", line 505, in <module>
    sys.exit(main(args.function))
  File "scripts/validate_docstrings.py", line 491, in main
    return validate_one(function)
  File "scripts/validate_docstrings.py", line 468, in validate_one
    examples_errs = doc.examples_errors
  File "scripts/validate_docstrings.py", line 265, in examples_errors
    for test in finder.find(self.raw_doc, self.method_name, globs=context):
  File "/usr/lib/python3.5/doctest.py", line 924, in find
    self._find(tests, obj, name, module, source_lines, globs, {})
  File "/usr/lib/python3.5/doctest.py", line 974, in _find
    test = self._get_test(obj, name, module, globs, source_lines)
  File "/usr/lib/python3.5/doctest.py", line 1058, in _get_test
    filename, lineno)
  File "/usr/lib/python3.5/doctest.py", line 660, in get_doctest
    return DocTest(self.get_examples(string, name), globs,
  File "/usr/lib/python3.5/doctest.py", line 674, in get_examples
    return [x for x in self.parse(string, name)
  File "/usr/lib/python3.5/doctest.py", line 636, in parse
    self._parse_example(m, name, lineno)
  File "/usr/lib/python3.5/doctest.py", line 695, in _parse_example
    self._check_prefix(source_lines[1:], ' '*indent + '.', name, lineno)
  File "/usr/lib/python3.5/doctest.py", line 792, in _check_prefix
    (lineno+i+1, name, line))
ValueError: line 11 of the docstring for pandas.option_context has inconsistent leading whitespace: '        ...'
```

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.

Two reasons to ignore the error with the whitespace:
1) It was there in the original, unmodified docstring
2) It appears to be an indication of the indentation following entering a `with` context block

Checklist for other PRs (remove this part if you are doing a PR for the pandas documentation sprint):

- [x] No related issue. Added to resolve a personal pet peeve (the original `option_context` api is extremely un-pythonic)
- [x] tests added & passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry (Not sure what to add or to which specific whatsnew file)

What's motivating this change? IIUC, this is equivalent to 

```python
opts = {'display.max_rows': 10}

with pd.options_context(*opts.items())
    pass
```

which isn't so bad. Though I could be missing something. Based on the compatibility issues, my own convenience isn't really worth this PR. I'll just rewrite the API entirely on my fork and keep it there so I'm not merging any breaking changes into the main repo