An example annotation processor

Testing Done:
Ran the target:

PANTS_DEV=1 ./pants goal bundle src/java/com/pants/examples/annotation/main

got the output in examples.txt
{
  {'type' : 'Main', 'value': 'Annotation Processing Example'},
}

Bugs closed: 131

Reviewed at https://rbcommons.com/s/twitter/r/372/