Allow data argument for GObject::Object#signal_connect
Fix spelling
Add threading example
Improve timeout example

Ensures regular timeout even under higher load: Timeouts should be
triggered every 10 ms even if the threads take up 9 ms. The idle handler
is only used once threads take more than 10 ms.
Add integration test for threading support
Add simple idle loop implementation
Automatically enable idle handler when MainLoop runs
Simplify main_loop example
More complicated thread enabler

Uses idle or timeout depending on usage.
Avoid creating a new handler every time
Simplify initializer
Simplify idle handler proc
Improve method naming
Ensure only one idle handler is ever present
Let Ruby threads run during GLib's main loop [merges 'threading-support']
Fix newly created RuboCop offenses