Changed Area to use a delegate handler object that implements the new AreaHandler interface for handling events. Also updated the GTK+ backend with this change, and made a few more tweaks to the documentation in area.go.
Updated the test program to the new AreaHandler interface. The deadlock still happens... just not so easily... so it's elsewhere...
Removed the mutexes from Labels and Areas because I'm at my wits end about settling the deadlock between window resizing and setting a Label's text.