Support CoffeeScript settings

Closes Issue #5

Notes on implementation:

- `settings.json` discarded in favor of `settings.coffee` (for future create actions & tests)
- `settings.json` still supported for backward compatibility (dugway still works with older themes using `settings.json`)
- dugway version bumped to `0.8.3`
- all tests updated & passing (including Travis build)
- `dugway create` && `dugway build` execute without error