Rename to Rapid.

This is a complete rebranding.  Some breakages may occur, as this was
mainly a global find and replace job.  Tests run, so hopefully it'll be
fine.
Gem-related fixes.
Rename the gem to ury-rapid.

A gem called 'rapid' already exists.
Gitignore pls
Merge pull request #36 from UniversityRadioYork/mw-rename-to-rapid

Rename to Rapid.