This ensures that recipes can simply be opened and built in-place using
C-c C-c, even if package-build had previously been initialized with a
different base directory.
See https://github.com/cask/cask/issues/236
- Add helper function `package-build-create-recipe`
- Add `package-build-minor-mode`, enabled for recipes: C-c C-c builds current recipe
- Opening recipe files causes `package-build` to get loaded, and
`package-build-minor-mode` to get enabled