additional types of channels for STM; documentation

 Additional types of STM channels:
  * TBChan: a version of TChan where the queue is bounded in length
  * TBMChan: a version of TChan where the queue is bounded in length
    and closeable.
  * TBMQueue: a version of TQueue where the queue is bounded in length
    and closeable.
  * TMChan: a version of TChan where the queue is closeable. This is
    similar to a TChan (Maybe a) with a monotonicity guarantee that
    once there's a Nothing there will always be Nothing.
  * TMQueue: a version of TQueue where the queue is closeable. This is
    similar to a TQueue (Maybe a) with a monotonicity guarantee that
    once there's a Nothing there will always be Nothing.
 .
 This package provides the documentation for a library for the Haskell
 programming language.
 See http://www.haskell.org/ for more information on Haskell.