Refresh doc section (and integrate with Docathon Sphinx template)

[arokem]

The parts of Shablona referring to documentation are in a pretty sad state.

Might be good to pull in things that are codified in @choldgraf's https://github.com/choldgraf/sphinx_template

The full wish-list (in order of priority):

• Replace what's in the docs folder now, with the most recent version of sphinx docs, and an explanation of how you might get to that point from an empty docs folder.

• Fix up README, to refer to gh-pages as the target for doc deployment, instead of RTD.

• Sphinx gallery, with an example in the examples folder.

• Integrate a gh-upload script for uploading from (for example): https://github.com/uwescience/pulse2percept/blob/master/doc/upload-gh-pages.sh
  with the make directive: https://github.com/uwescience/pulse2percept/blob/master/doc/Makefile#L187-L188

I'd prefer the latter to auto-deployment from Travis, because I found that auto-deployment from master tends to confuse users that installed the released software (e.g., from PyPI). But am open to discussion on the topic.