Version 0.5.0

Added

• composer func which creates composer functions that accept an array of middleware
  and compose into a handler.
• guard a generic middleware that will throw an exception when invoked to indicate an
  error in logic.
• guardedComposer decorator to automatically add guards when composing a middleware stack

Changed

• Moved MwStack to simply Stack and simplified the API
• Removed Pimple integration in favor for the PSR container.