PROTON-227: Created the Data class for the Ruby bindings.

The APIs are more Ruby-esque, replacing most of the put_type methods
with type=, and get_type with type.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1450219 13f79535-47bb-0310-9956-ffa450edef68