[#70889056] refactor emitters to use []byte instead of Event

(in preparation for sharing emitters with agent)

Signed-off-by: John Tuley <jtuley@pivotallabs.com>
[#70889056] extracted common libs into separate repo

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Reinstate coverage in tests

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>