Setup readthedocs.org documentation

[ddemidov]

This was branched off version-updates so as not to loose any recent work by @WasabiFan. Hence the first three commits here.

This PR does a couple of things:

1. Switches from markdown to reStructured text for the READMEs.
2. Creates the docs folder with Sphinx configuration and a couple of reStructured text files. Some of them just import the original READMEs, some (actually, just classes.rst) are generated from spec.json, and others contain supporting hand-written text (mostly split out from the removed human-readable-spec.md).

I've also created a project on readthedocs.org, and added the corresponding webhook to this repo. This way documentation on readthedocs.org will be autoupdated after each commit here. I have already added @rhempel as a maintainer of readthedocs project; @WasabiFan, if you tell me your username there, I'll add you as well.

The result looks like this: http://ev3dev-lang.readthedocs.org.

In order to generate the documentation locally, one needs to install Sphinx and Sphinx Bootstrap Theme, and then do

cd docs
sphinx-build -b html . /path/to/generated/html

The html documentation will be created in the specified folder, which will be created if necessary.

Also see #146.

[WasabiFan]

Looks good to me; feel free to merge if you believe it's ready.

Can you post a list of the information that isn't included yet? I can't quite tell from the diff.

[ddemidov]

This has the same TODO list as the one in #146. All I did was convert to the new format. I'll merge this anyway, so that new work may be done in the new format.

[WasabiFan]

OK, that's how it looked, I just wasn't sure. I'll update it when I can.