Support for using uvector's MUArrs in the new ST monad. Reexports all of Data.Array.Vector's API, but all the ST operations are done with the new ST monad.

Notable differences in API:

• the former unsafeFreezeMU is in fact safe, and is now named freezeMU.
• similarly for unsafeFreezeAllMU
• newU is no longer required as a primitive; it can be implemented using runSTT and freezeAllMU, mentioning no unsafe operations.

Example demonstration of using the new ST monad:

foo :: (UArr Int, UArr Int)
foo = runST go where
  go :: forall s. ST (Normal s) (Freeze s) (UArr Int, UArr Int)
  go = newMU 5 >>>= a1 ->
       newMU 6 >>>= a2 ->
       writeMU a1 0 3 >>>= () ->
       writeMU a2 1 2 >>>= () ->
       freezeAllMU a1 >>>= v1 ->
       freezeAllMU a2 >>>= v2 ->
       return (v1,v2)