GH-422 Improvements in cloud event samples

Added initial README
Polished tests

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

@@ -0,0 +1,71 @@
+## Cloud Events with Spring samples
+
+### Introduction
+The current example uses spring-cloud-function framework as its core which allows users to only worry about functional aspects of 
+their requirement while taking care-off non-functional aspects. For more information on Spring Cloud Function please visit 
+our https://spring.io/projects/spring-cloud-function[project page].
+The example provides dependency and instructions to demonstrate several distinct invocation models:
+
+ - Direct function invocation
+ - Function as a REST endpoint
+ - Function as message handler (e.g., Kafka, RabbitMQ etc)
+ - Function invocation via RSocket
+ 
+The POM file defines all the necessary dependency in a segregated way, so you can choose the one you're interested in.
+ 
+#### Direct function invocation
+
+#### 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>)
+
+Here is an example of curl command posting a cloud event in binary-mode:
+
+[source, text]
+----
+curl -w'\n' localhost:8080/asPOJO \
+ -H "ce-Specversion: 1.0" \
+ -H "ce-Type: com.example.springevent" \
+ -H "ce-Source: spring.io/spring-event" \
+ -H "Content-Type: application/json" \
+ -H "ce-Id: 0001" \
+ -d '{"releaseDate":"24-03-2004", "releaseName":"Spring Framework", "version":"1.0"}'
+----
+
+And here is an example of curl command posting a cloud event in structured-mode:
+
+[source, text]
+----
+curl -w'\n' localhost:8080/asString \
+ -H "ce-Specversion: 1.0" \
+ -H "ce-Type: com.example.springevent" \
+ -H "ce-Source: spring.io/spring-event" \
+ -H "Content-Type: application/cloudevents+json" \
+ -H "ce-Id: 0001" \
+ -d '{
+    "specversion" : "1.0",
+    "type" : "org.springframework",
+    "source" : "https://spring.io/",
+    "id" : "A234-1234-1234",
+    "datacontenttype" : "application/json",
+    "data" : {
+        "version" : "1.0",
+        "releaseName" : "Spring Framework",
+        "releaseDate" : "24-03-2004"
+    }
+}'
+----
+
+#### Function as message handler (e.g., Kafka, RabbitMQ etc)
+
+Streaming support for Kafka and Rabbit is provided via Spring Cloud Stream framework (link). In fact we're only mentioning Kafka and Rabbit here as an example.
+Streaming support is automatically provided for any existing binders (e.g., Solace, GCP, AWS etc) (link)
+Binders are components of SCSt responsible to bind user code (e.g., function) to broker destinations so execution is triggered
+by messages on broker destination and results of execution are sent to broker destinations. Binders also provide support consumer 
+groups and partitioning for both Kafka and RabbitMQ messaging systems. 
+
+
+#### Function invocation via RSocket
+
+TBD