Added coproducts.
Isos reworked in terms of Generic.
Coproducts now have a terminating CNil.
Removed CNil case object.
Removed CNil methods.
Major rework of Scrap Your Boilerplate, fixing many bugs and supporting
traversal through (recursive) subtypes.
Added Scrap Your Boilerplate Tree example.
Bumped version to 2.0.0-SNAPSHOT.