Several small fixes:
 - More robust handling of relative filepaths in 'open' and 'save'
   commands
 - Switch buffers when calling 'open' instead of setting buffer contents
 - Allow a subscriber pane to break an existing link when switching buffers
 - Small documentation updates
 - Fix incorrect placement of a forced reflow in StatusLight.fadeIn()
 - Trigger a focus/blur event when a pane's focus state changes