Split layer docs

[f0k]

This splits up the lasagne.layers Sphinx documentation across multiple pages; one per submodule (but taking care to present all classes as belonging to the lasagne.layers namespace if appropriate). It requires Sphinx 1.2.3 to build because of a regression in more recent versions (see #203 (comment)), but we use that one on readthedocs anyway (just note that a more recent version will omit the autosummary tables, so make sure to use Sphinx version 1.2.3 or the latest git version if building locally).

I've tried a few different options for the TOC and layout, and this is the best I found. It has a bunch of autosummary tables for lasagne.layers, and the TOC is set up such that clicking Convolutional layers in the left-hand navbar takes you to the detail page for convolutional layers, not to the autosummary table within the lasagne.layers overview page (mainly because then we'd either have a second navbar entry for the detail page or have Sphinx whine about the detail page not being included in any TOC).

Finally, I did some minor docstring fixes that triggered Sphinx warnings or caught my eye in the overview page.

[benanne]

lgtm, I don't have time at the moment to review this in detail though. If you want to be on the safe side better have someone else check as well. Otherwise I'm okay to merge.

[f0k]

All right, if anybody has the time to take a look, the following should do the trick:

git checkout -b f0k-split-layer-docs master
git pull https://github.com/f0k/Lasagne.git split-layer-docs
cd docs
make clean html
firefox _build/html/index.html &

Make sure to do pip install Sphinx=1.2.3 sphinx_rtd_theme if you have a different sphinx version.

[f0k]

I've amended the first commit to include sphinx_rtd_theme in requirements-dev.txt. I hope readthedocs won't bark on this. I'll still wait with merging until #294 is merged, so the latter doesn't need to be rebased again. I'll rebase this one afterwards.