Added `depend_on_asset` comments

Ensures Sprockets includes during compilation

via
[sprockets_better_errors](https://github.com/schneems/sprockets_better_errors)
Use `asset_path` helper in coffescript

For integration with sprockets digests
complies with sprockets_better_errors
Merge pull request #2 from seanpdoyle/master

Added `depend_on_asset` comments