Bumped version to 0.13.1.
Added empty product tests.
Improved logic for handling Generic[Unit].

+ Eliminated some duplicated code in Generic.materializeXXX.
+ Added TypeClass tests for Unit and tuples.
Added Scalding PoC example.
Updates for latest 2.11.0-SNAPSHOT changes.
* Commented out lifted Poly tests which currently don't compile.
Merge branch 'master' into scala-2.11.x

Conflicts:
	core/src/main/scala/shapeless/generic.scala