Improved error reporting using Promise.done
Improved error reporting using Promise.done

Proper error reporting in gulp depends on exceptions thrown at the top
level.  Apparently the stream callback will throw such an error in a
synchroneous fashion.  So we must not call the callback in a situation where
errors get caught by the promise machinery.  Promise.done can achieve this.

philmander/gulp-hbs,philmander/gulp-hbs