[ruby-binding] the package name on rubygems.org does not follow conventions

The rubygems.org name is currently qpid_proton. From a not-so-random sampling, it seems to me use of dashes is more common than that of underscores. Additionally, the package in PyPi is called python-qpid-proton.

I propose renaming the ruby package to qpid-proton or ruby-qpid-proton or even qpid-proton-ruby. If possible, which it may not be, by now.