Add MsgPack serialization
Replace CityHash with MD5, update cache key format
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lib/cacheable/middleware.rb
	test/cacheable_test.rb
	test/middleware_test.rb
Deal with non-hash key/version keys
Some code cleanup
Major version bump
tests: Add a ControllerTest and move a relevant test to it.
Add a Cache-Control no-store header for uncacheable requests.