Reworking of Poly infrastructure and namespacing.

- Free standing CaseNAux is now CaseN
- Free standing PullbackNAux is now CaseN.Aux
- Poly#CaseN is now PolyN#Case
- Most auxilliary definitions have been moved into object PolyDefns
  which has a val alias in the shapeless package object allowing
  access via 'import poly._'
- The miscellaneous Poly examples have been moved to either examples or
  tests. The identity Poly has been moved to poly._.
- ~>> is now a type alias for ~> with a constant type constructor on the
  RHS
- ~?> is used almost exclusively with HMap, so it has been moved to
  HMap's source file.
- LiftO is now an example. Use liftA from shapeless-contrib instead.
Removed all uses of deprecated API.
Removed deprecated API. Definitions are retained on the deprecated branch.
Record fields are now properly widened to their value type when viewed as values.
Updated contributors list.
Bumped SBT version to 0.13.0-RC5.
Bumped SBT version to 0.13.0 final.
More descriptive compilation failure message
Merge pull request #45 from jonifreeman/record-error-msgs

More descriptive compilation failure message for invalid record access
Made DepFn2 and HList's Prepend contravariant
Merge remote-tracking branch 'upstream/master'