The example config now additionally demonstrates how to use a shell loop
to create a mapping in multiple modes, how mediakeys can be mapped and
how to use the "None" modifier.
This command takes a mode, modifiers, button/event name, and pointer
action as arguments. It stores these in the config data structure.
The currently available pointer actions are move-view and resize-view,
which replace the previously hard-coded functionality.
Closing the hovered view with middle click has temorarily been removed
until it is decided if we wish to make this another special pointer
action or perhaps allow running any arbitrary command (which would of
course include close).
