Changes

Implement CanonicalOverwrite

Also refractored the place where element remappers are stored.
Instead of all being inner classes of AnnotationRemapper, they
are now stored in their own package.

This change also caused some methods to be now public.
However, they should not be treated as public API and have been
marked as internal API accordingly.

This change makes it easier to manage the introduction of new
annotations.
 (commit: 53fff35)