Plugins: Created processingComplete event

The processingComplete event fires after all processing has been
done. It gets the entire docs as its only parameter.
processingComplete event: covered by unit tests

The processingComplete event now contains an object with the docs array under the 'doclets' key. The event is now covered by a unit test.
Merge pull request #421 from ErnstHaagsman/processingcomplete-event

Plugins: Created processingComplete event