gen_doc.sh: fix to apply to py/, not specific dirs

Make this easier to maintain by implicitly applying to 'py/*' instead of
explicitly stating dir names.

Generate previously accidentally excluded 'py/gab'.

'cd' to same dir as script file so it works from anywhere.
(same as the other precommit scripts do)

Test Plan: $ ./gen_doc.sh
static_tests: fix to apply to all 'py/'

Update 'static_tests.sh' to apply to all scripts under 'py/' without
having to explicitly enumerate the dirs to apply to.

Fix up errors that were previously missed in modules that weren't
covered.

Test Plan:
Introduce error in gabcmd_gitphablog.py, ensure spotted by
$ ./static_tests.sh

Just in case
$ ./precommit.sh