Juwang-http avro serilazer

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 request contains the following:
1. add Avro schema for HttpRequest, 
2. add AvroHttpSerializer class that does serialization and deserialization for JSon string and bytes.  
3. Some other changes such as to make getUriSpecification public for client in other modules to access. 
4. Test cases for AvroHttpSerializer are included.  
5. reformatting for the code.