another step on the road of getting rid of overlays altogether (they are
full of special cases; popups and menus are to go also eventually). We
lose some of the styling of borders but gain the ability to run
display-panes in another pane (perhaps not hugely useful but one never
knows). The -b flag goes away as no longer useful.
additional payload (to reduce problems with lifetime of objects) and are
delivered to one or more event sinks. This is more powerful and reduces the
complex dependencies between control mode and hooks. Events are now used for
hooks, control mode notifications and for monitors (set-hook -B).
wait-for can now wait for an event to fire (-E flag, with -F to for filter),
with -v to print the payload, as well as listing (-l) waiting clients on an
event and forcing one to wake (-w).
A few additional hooks are also now available (pane-created, pane-resized, etc)
and some of the existing ones have additional format variables available.
