Added alternative async and withAsync functions

This makes the API consistent with Control.Concurrent:

 - asyncBound
 - asyncOn
 - asyncWithUnmask
 - asyncOnWithUnmask

 - withAsyncBound
 - withAsyncOn
 - withAsyncWithUnmask
 - withAsyncOnWithUnmask
Merge pull request #2 from basvandijk/complete

Make the API consistent with Control.Concurrent
small optimisation
add Functor instance
bump to 2.0.1.0
note about the Functor instance
add Changes
benchmark tweaks
add Concurrently, mapConcurrently
tweak to docs
more Changes
Add Trustworthy; bump to 2.0.1.1
bump stm dependency
bump base dependancy; don't hide Prelude.catch for base>=4.6; bump version to 2.0.1.3
Merge pull request #3 from hvr/ghc76

Fix compilation for GHC-7.6.1
base dependency of the test suite was not updated.
Merge pull request #4 from nomeata/patch-1

base dependency of the test suite was not updated.
bump to 2.0.1.4
add
Making the library compile with GHC7.7