Add support for asynchronous DummyApi replies.
Allow async to be made the default when constructing an ImTester.
Add tests for async test_utils (this required pulling in Q, a promises implementation with error handling).
Add comment describing how pending_async works.
Add test that async DummyApi fires calls asynchronously.
Make return of DummyApi kv.get match that of the real KV resource in the cases where the value is not present in the KV store.
Merge branch 'feature/issue-16-asynchronous-dummy-api' into develop
Better error messages for required parameters to check_state and check_close.
Print out better messages when asserting in test_utils.
Add messages to all assert calls.
Fix error messages for state checking.
Add comments about the supported resources.
Add implementations of contact resource methods.
Remove TODOs as unnecessary for now.
Test contacts.get.
Add test for contacts.get failure case.
Add tests for contacts.get_or_create.
Also check created field in replies to contacts.get_or_create.
Add tests for contacts.update.
Add tests for contacts.update_extras and contacts.update_subscriptions.