setup.py: If `build_sphinx` is specified, run `sphinx-apidoc` first to generate the `rst`. Fixes jakirkham/nanshe#197.
setup.py: If `build_sphinx` is specified, run `sphinx-apidoc` first to generate the `rst`. Fixes jakirkham/nanshe#197.

DudLab/nanshe,nanshe-org/nanshe,jakirkham/nanshe,DudLab/nanshe,jakirkham/nanshe,nanshe-org/nanshe