Rake-based build process.

Don't feel any obligation to take this into the repo, but I thought it might be good to have it running on the same process as Simple.Web, especially for CI. I also wanted to see how long it would take me to convert a repo.

**Note:** I used `git mv` again and checked it showed moved files as 'renamed' in the hope it doesn't lose the source history as it seemed to do in Simple.Web; if it does then I can only think it's the pull-request merge on github causing it.