Juwang http avro serilazer bridge

To send Http Request/response data cross the Java/C# bridge, the data needs to be serialized at one side and deserialized on the other. This change added Avro schema for HttpRequest, added AvroHttpSerializer class that does serialization and deserialization for JSon string and bytes.  
Test cases for AvroHttpSerializer  are included.  
The change in the branch is merged from juwang-httpAvroSerilazer (branched from master) and juwang-reef-bridge-HttpAvro-Serializer (branched from reef-bridge). This is a clean version.