Add some actual sphinx documentation. This is basically the README
split up into sections. Once this is actually published somewhere,
we can remove some of the content from the README and link to an
on-line reference instead.
This fixes the tox configuration for the flake8 target.
It excludes all existing flake8 issues, so the flake8 target succeeds.
In the following commits, I will fix these flake issues individually,
and remove the corresponding exclude from the list, so that every commit
passes the flake8 test.
It also adds the generated .tox folder to .gitignore.
If you set up a virtualenv in gertty-env according to the instructions
in the readme, it shows up as an untracked folder. Add it to the ignore