MonadWriter for IterT (not proved to be correct)
removed redundant Functor m constraint
fixed MonadWriter instance for listen-tell law
a bit more readability for MonadWriter IterT instance
MonadWriter instance for FreeT
Merge branch 'master' into writer

Conflicts:
	src/Control/Monad/Trans/Iter.hs
MonadWriter instance for FT
Merge pull request #45 from fizruk/writer

MonadWriter instances for free monad transformers.