Document images.
Move ObjectDiff into util
Move Codec functions to their own file
Merge pull request #1690 from erictune/image_docs

Document images.
Merge pull request #1693 from smarterclayton/move_diff

Minor moves of functions into their own files
Genericize MetaInsertionFactory into a simpler interface

The common path code for MIF goes through a conversion cycle - it
can also be done through reflection. This simplifies the Create/Update
methods into Interpret (return version) and Update (through reflection).

In addition it uses only one MetaFactory implementation across all of
our packages which reduces a bit of duplication.
Use one copy of EnforcePtr
Remove unused code
Move FindTypeMeta into the proper file