Log Message:
This package provides combinators for sequencing IO actions onto a thread
pool. The thread pool is guaranteed to contain no more unblocked threads
than a user-specified upper limit, thus minimizing contention.

Furthermore, the parallel combinators can be used reentrantly - your
parallel actions can spawn more parallel actions - without violating this
property of the thread pool.

The package is inspired by the thread
http://thread.gmane.org/gmane.comp.lang.haskell.cafe/56499/focus=56521.
Thanks to Neil Mitchell and Bulat Ziganshin for some of the code this
package is based on.