Add method to extract event_message from event

[codylerum]

Currently there is not a means to get an event message from an event.

This can be found in an event_metadata on an signature_request_invalid event

"event_metadata":{"related_signature_id":null,"reported_for_account_id":null,"reported_for_app_id":"xxxxxxx","event_message":"Text tags error: No signers in text tags"}}

[codylerum]

@cmpaul Any hints as to how to run the test-suite locally?

[cmpaul]

@codylerum Sorry for the delay, this looks good! Thank you!

As for tests, they are rather complicated to run as they require live access to the API with certain conditions met (templates with specific fields). I have an issue open to streamline these, remove the need for a live connection, and hook them up to travis-ci (Issue #13).

[codylerum]

👍 for Travis CI