Event stream protocol tests

[JordonPhillips]

This adds a trait for event stream protocol tests as well as an initial batch of tests for restJson1. These can be used to assert an implementation is compliant with the protocol.

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[sugmanue]

Probably there are some below, but if there aren't, I'd be good to test malformed input, e.g, invalid type (boolean given where string expected), and similar.

[JordonPhillips]

Regarding blobs - in existing protocol tests we do not base64 encode byte strings. I this test, for example, you can see that the byte string data in params is not encoded. It is encoded in the body bytes because that is how it is expected to be within the JSON. These tests don't have the raw value of the headers, so there's nowhere to show its encoded form.

EDIT: I changed my mind on this. The tests that don't have base64 representing bytes should. That can't be changed now, but we don't have to introduce more of this.

One addition that was made to the spec was to allow including the entire event bytes. These tests were written before that, so they aren't there. But I can add them. It's not really useful for serialization comparisons, but it is useful for deserialization tests, so I can go ahead and add them.