add eitherTPlus, eitherTMonadPlus. fix EitherT#filter, EitherT#withFilter

https://groups.google.com/d/msg/scalaz/NCiRRxLjanM/zArkn18vScgJ
https://github.com/ekmett/either/blob/v4.0/src/Control/Monad/Trans/Either.hs#L147-L163
EitherTTest
Add Free.liftF - lifts a value from within a Functor into Free

    scala> scalaz.Free.liftF(Some(1): Option[Int])
    res1: scalaz.Free[Option,Int] = Suspend(Some(Return(1)))
Merge pull request #618 from puffnfresh/free-liftf

Add Free.liftF - lifts a value from within a Functor into Free
Merge remote-tracking branch 'xuwei-k/eitherTMonadPlus' into scalaz-seven
Specialized biases for Bi{functor,foldable,traverse}.
Functions for combining type parameters on bifunctorial typeclasses.