PROTON-531: Removed Selectable.killable? from Ruby bindings

The API is unnecessary.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1589121 13f79535-47bb-0310-9956-ffa450edef68
prototype on pom
Flow Control Callback
protoype on Parser
buffer idea refactoring