Add invoke task for publishing to PyPI.

And Crate!
Bump version to 0.1.0a1.

This makes it compatible with PEP 386 and also simplifies publishing
in-progress versions to PyPI (by merely incrementing the alpha number).

Thank you Crate for complaining about this.

Now let's see if we can get Read the Docs to do versions.
Add distutils-generate files to .gitignore.