GH-422 Formalize Cloud Event conversion strategy to consistently handle binary-mode and structured-mode cloud events

Moved CloudEvent related artifacts to ‘cloud events’ package with hopes to eventually donating it to CNCF SDK
Created CloudEventUtils identifying necessary constants and utility methods

spring-cloud-function-samples/function-sample-cloudevent/README.adoc

@@ -38,7 +38,24 @@ provides a good example on how to accomplish this.
 ### Function as a REST endpoint
 
 Given that SCF allows function to be exposed as REST endpoints, you can post cloud event to any of the 
-functions by using function name as path (e.g., `localhost:8080/<function_name>`)
+functions by using function name as path (e.g., `localhost:8080/<function_name>`).
+
+Just add this to your dependency
+
+[source, xml]
+----
+<!-- REST - only needed if you intend to invoke via HTTP -->
+<dependency>
+	<groupId>org.springframework.boot</groupId>
+	<artifactId>spring-boot-starter-web</artifactId>
+</dependency>
+<dependency>
+  	<groupId>org.springframework.cloud</groupId>
+  	<artifactId>spring-cloud-function-web</artifactId>
+  	<version>3.1.0-SNAPSHOT</version>
+</dependency>
+<!-- end REST -->
+----
 
 Here is an example of curl command posting a cloud event in binary-mode: