Tests for the length method of HLists
Fix in Length implicits

- Makes HNil.length compiles
- Adds HNil.length to the tests
Added method .toHList to Sized
Added method .toSized[M] to HList and tuples
Merge pull request #114 from alexarchambault/master

HNil.length / Sized.toHList / HList.toSized[M]