put mock WSGI app state in objects for each test module
use context manager for test install/uninstall

allows us not to use reset(), just get a fresh InstalledApp
reduce InstalledApp boilerplate

test modules don't have to subclass BaseInstalledApp
merge MockWSGIApp into InstalledApp for simpler use
plumbing for sphinx docs
docs content
module docstring tweaks
Merge pull request #14 from sashahart/sphinx_docs

Start at sphinx docs
Merge pull request #12 from sashahart/test_overhaul

Test overhaul to reduce global state.