Merge branch 'release/2.3.3' into develop
[BUGFIX] Process signals safely in the main thread

One can't do jack in a signal handler on Ruby 2.0
[CS] Don't override respond_to?

This is what respond_to_missing? is for
[CS] We don't use future-resource directly
[DOC] Document that #dial confirmation_metadata is shared/unsafe
[BUGFIX] Expose the cert store directory in Punchblock config

Fixes #309
[BUGFIX] #respond_to_missing? takes two args

We should have test coverage for this, dammit! Coming soon.
[BUGFIX] Add test coverage for Events.respond_to? and fix for good
[BUGFIX] Abort initialisation if Punchblock fails to connect
[DOC] Clearer changelog
[UPDATE] Bump to 2.3.4
Merge branch 'release/2.3.4'