MANIFEST: Include a lot more missing stuff in the manifest

Versioneer needs to be in the MANIFEST.in and its .pyc needs to be ignored
in the .gitignore.  Also much docs were not being included, nor conftest.py.
Much of the test suite data files needed including, so changed that to a
raw include of everything in the tests/ tree.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>