Added structural implicits for Length.
Added structural implicits for Size.
Renamed implicit methods in Length.scala to be consistent with naming in Size.scala.
Cleanup previously commented code in Length.scala and Size.scala, and comments out implicits that are no longer required.
Merge branch 'duck-length-size' of https://github.com/cheeseng/scalatest
Uncommented the nominal type implicits for Length and Size.