Add an enabled option (defaulting to true) to allow the add-on to be turned on and off (based on the environment, for example).
Make this add-on run before broccoli-asset-rev.

broccoli-asset-rev is included by default with ember-cli, and may mess with
filesystem lookup.
Update to new format for add-on definition.
Merge branch 'before-asset-rev'
Merge branch 'update-plugin-format'

Conflicts:
	index.js