Fix spelling
The big rename: git-hub is now git-spindle

git-hub is being renamed for two reasons:

- I plan to add support for BitBucket and GitLab
- GitHub legal requested I do so for trademark reasons

So I took advantage of this semi-forced rename (GitHub was quite nice
about it) and restructured the code to make the goal of adding GitLab
support easier.

Usage does not change, it should be 100% backward compatible