Config parsing, factory, and hooks for post processing.
Merge remote-tracking branch 'origin/master' into jh-post-processing
Remove old post-process config handling and add comments.
Improve handling of post_processor.
Internal restructure in post_processor.
Renamed mergenizer to unionizer.
Fix segfault when config specifies invalid izer types.
Merge pull request #6 from MapQuest/jh-post-processing

Post-processing