Add API documentation using pdoc
Summary
Add API documentation using pdoc
A lot of documentation is missing but it's a start. If we need more complicated features in the future we can move to Sphinx but pdoc is great and a very small dependency.
Remove unused import
This also checks for the existence of a 'python' binary. It assumes it's Python 2.7 if found and uses it. If it's not found it skips building the documentation instead of erroring out.
Once we drop Python 2.7 support we can set this up properly using Wafs internal Python detection. It's non-trivial to pickup and support two versions at the same time.