Add GooglePreprocessor and SmartPreprocessor

[vemel]

GooglePreprocessor - supports Google format for docstrings
SmartPreprocessor - wisely chooses between RST and Google preprocessors for each docstring

[NiklasRosenstein]

Please go back to two-space for this PR so I can properly review the actual changes. We can think about converting the code base to four-space in another PR.

[NiklasRosenstein]

Please also be aware that I'm working on a new version that parses the code with lib2to3 instead of executing the code on the develop branch. It's actually not far from being merged into master and 2.x being moved into its own branch.

Anyway, happy to merge your PR into the 2.x code base. I'll likely copy the processor code to the 3.x branch afterwards.

[vemel]

Rebased to master, should be no conflicts now.

[NiklasRosenstein]

Please take a look at the pr-84 branch. I've added some unit tests. Could you take a look at why the smart preprocessor does not detect the Google syntax properly? 😃

[vemel]

I will take a look, thanks! Actually, I implemented GooglePrerocessor incorrectly, it also supports https://www.python.org/dev/peps/pep-0257 we should probably split these two guys, and we can create a parent class for them as methods will be the same, just param regexps should be different.

FOr now logic for detecting docstring style is quite simple. If I find a section from Google/PEP-0257 -
(e.g. Args:) I use GooglePreprocessor. Otherwise, RST is used.

[vemel]

Please take a look at the pr-84 branch. I've added some unit tests. Could you take a look at why the smart preprocessor does not detect the Google syntax properly?

Fixed, regexp was incorrect.