CloudEvents I/O format support. (#948)

* CloudEvents I/O format support.

* Updated format doc.

* Remove log lines

* This adds support for CloudEvent ingestion at the http router layer.

* Updated per comments.

* Responds with full CloudEvent message.

* Fixed up per comments

* Fix tests

* Checks for cloudevent content-type

* doesn't error on missing content-type.

api/models/call.go

@@ -23,6 +23,8 @@ const (
 	FormatHTTP = "http"
 	// FormatJSON ...
 	FormatJSON = "json"
+	// FormatCloudEvent ...
+	FormatCloudEvent = "cloudevent"
 )
 
 var possibleStatuses = [...]string{"delayed", "queued", "running", "success", "error", "cancelled"}