Use py.test to launch pytest, rather than python -m test, preventing the empty path from being added to sys.path per pytest-dev/pytest#2104. Fixes #852. Also use 'usedevelop' as the setuptools.tests.fixtures aren't available in a standard install.

docs: reorder ToC; update stray Bitbucket links

Metadata and options are now could be set in configuration files

Spelling fixes

Tell unittest.main not to exit, fixes #850.