Implemenet common API for bidirectional conversion between higher level...

Implemenet common API for bidirectional conversion between higher level language objects and C++ Hive protocol structures

- val_protocol.hpp - Convert higher level objects to C++ Hive protocol
  structures using either protobuf or standard structure
- proto_converter.hpp - Directly convert higher level object API
  representation of the object to the proto one (directly modifying the
  object)
- api_converter.hpp - Directly convert higher level object proto
  representation of the object to the API one (directly modifying the
  object)