Let travis.ci run tests on modern rubies
Update dependency on gir_ffi

This stops Gtk::Builder#connect_signals_full throwing an error.
Remove deprecated RR Adapter, silencing warning
Always generate coverage report
Trust test task to include lib in the load path
Clean up base overrides file
Load menu overrides file from top level required file
Test overrides for both Gtk+ 2 and 3 by default
Only provide and test Gtk::Menu#popup if needed
Simplify loading of test helpers
Provide overrides for Gtk::RadioButton constructors on Gtk+ 2.0
fixup! Simplify loading of test helpers
Simplify Rakefile
Make pry available in local development environment