Added Prefix class.
Added Prefix.__eq__
Added Prefix.__lt__
Refactored ID to use Prefix.
Implemented constructor identity for ID/Prefix.
Applied the Prefix class.
Merge pull request #54 from jacebrowning/type-cleanup

Clean up types that always use .lower()
Only checking levels if not reordered.
Added '--no-level-check' setting.
Merge branch 'master' into profiling