Pushy v0.14.1 - bug fixes and cleanup

This release is a grab-bag of fixes, cleanup, and improvements. The highlights:

• Fixed a potential bug where we'd continue to try to recover from an expired authentication token even if the server considered the connection permanently invalid
• Significantly improved the performance of our JSON parser
• Use Optional to convey that timestamps in push notification responses won't always be present

For a complete list of changes, please see the v0.14.1 milestone.