Add Pipes.Prelude benchmarks.

Minimum Cabal version required by 'Default-Language' is 1.10
Merge pull request #59 from merijn/master

Add mtl instances for MonadReader, MonadWriter and MonadState.  Fixes #56
Merge pull request #60 from archblob/benchmarks

Add complete Pipes.Prelude benchmarks.
Added 'map' and 'filter'

... at the request of Nimish Telang
Merge branch 'master' of github.com:Gabriel439/Haskell-Pipes-Library
Tighted up documentation in Pipes.Prelude
Fixed 'foldM' to match the signature necessary for the `foldl` library
Added `length` fold
Changed 'debug' to be a 'Pipe'
Removed 'yieldIf'
Upgraded 'chain' to a 'Pipe' and removed 'debug'
Changed 'read' to be a 'Pipe'
Removed replicate and replicateM
Moved Consumer section above Pipes section of Pipes.Prelude
Changed `Producer'` type synonym to restrict downstream input
Added `foldl` support to `pipes`
Renamed `foldl` to `fold` and `scanl` to `scan`
`await` and `yield` now use `Consumer'` and `Producer'` type synonyms
Updated documentation
Re-exported polymorphic type synonyms from the `Pipes` module