Fix doctests
Hack code generator
Add basic Issues, Labels and Milestones
Add todo
Extract from https://github.com/github/developer.github.com/commit/f950e84a0c0161b312a550004a2ecd9791f7bb36
To be reverted: temporary unimplement POST /repos/:owner/:repo/git/trees

We have no test (yet) for this API, so reduce noise in missing
test coverage.
Fix doctests
Fix doc generation
Add (depressing/motivating) info in generator