An abstract interface to highly-parameterizable queues/deques.

Background: There exists a feature space for queues that extends
between:

  * simple, single-ended, non-concurrent, bounded queues 

  * double-ended, threadsafe, growable queues

... with important points inbetween (such as
the queues used for work-stealing).

This package includes an interface for Deques that allows the
programmer to use a single API for all of the above, while using
the type-system to select an efficient implementation given the
requirements (using type families).

This package also includes a simple reference implementation based
on 'IORef' and "Data.Sequence".
