DOC: Fix broken formatting on docstring examples with first-line comments
Examples for `interpolate` and `groupby` weren't being formatted correctly. See http://pandas.pydata.org/pandas-docs/version/0.16.0/generated/pandas.Series.interpolate.html and http://pandas.pydata.org/pandas-docs/version/0.16.0/generated/pandas.Series.groupby.html

Thanks for noticing! But, the 'correct' solution is that there should be a blank line between the explanation and the code. In this way the `code-block` is not needed, which looks a bit nicer in raw format.

Also the `#` is not needed then, so this can be removed as well.

see https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections for a reference
 But very welcome to update the PR!
 @jorisvandenbossche ?
 Yes, forgot about this. 
@evanpw Is looking good! Can you squash?
 Squashed
 Thanks!
