Squishy 2.0

API updates to integrate cleanly with Scala 2.10:

• Moved from using scala.parallel.Future to scala.concurrent.Future
• Completely removed squishy.Callback in favor of using the operations on scala.concurrent.Future
• Changed the squishy.AsyncQueue API match that of squishy.SyncQueue
• Moved from using (Long, java.util.concurrent.TimeUnit) to scala.concurrent.Duration
• When an operation is performed on a non-existent queue, Squishy now produces a
  com.amazonaws.services.sqs.model.QueueDoesNotExistException instead of a java.lang.IllegalStateException

Internal changes to make use of Scala 2.10 features:

• Internal use of the scala.concurrent packages for implementing asynchronous behavior
• Switch to using string interpolation as opposed to String.format

Other Improvements:

• Added tests for squishy.RetryPolicy
• General code cleanup and removal of boilerplate
• Reworked the examples to be safer and more idiomatic.