add Cofree instances
CofreeTest
add explicit return type annotations
Iso3#unlift, unlift1, unlift2 and Iso2#unlift
use unlift
fix Traverse#traverseS, sequenceS, traversalS

avoid stack overflow
Traverse#sequenceS, traverseS, traversalS test
Merge pull request #616 from xuwei-k/traverseS-trampoline

fix Traverse#traverseS, sequenceS, traversalS
Merge pull request #613 from xuwei-k/iso-unlift

Iso3#unlift, unlift1, unlift2 and Iso2#unlift
Merge pull request #610 from xuwei-k/cofree-instances

Cofree instances