Switch setup.py to python-versioneer.
Generate the versioneer artifacts with `setup.py versioneer` - necessary only when first switching to python-versioneer or when upgrading to a new version of python-versioneer.
Get rid of the old version export.
Merge pull request #19 from exarkun/versioneer

Replace manually managed version number plus `import imaginary` in setup.py with python-versioneer.