Implements the CloudEvents Spec v0.3

Fixes: cloudevents#25

Fixes: cloudevents#23

Paying the technical debt

Release for the issue cloudevents#18

Release for the issues: cloudevents#11, cloudevents#17, cloudevents#18.…

… PRs: cloudevents#16 and cloudevents#15

Release for the issue cloudevents#7, PR cloudevents#10 and cloudevents#8

Release 0.2.0 - http binding binary 0.2

Merge pull request cloudevents#3 from cloudevents/spec0.2

Specification 0.2 support