Remove the view controller reference in behaviour consts.
Add a global monitor for transient behaviour.

This means we correctly mimic NSPopover's behaviour of closing when
there is a click anywhere outside of the popover view.
Close transient popovers when the app resigns active.
Don't listen for the escape key in the global monitor.
Add initial support for semi transient.

This clones the behaviour of NSPopover such that mouse _up_ events
within the popover's window will close it.

We currently don't match NSPopover in one aspect: it doesn't close if
the user moves the window.
Support semi transient with multiple windows.
Update docs.
Application defined typo --
This is Rebel… not AppKit.
Strong transient event monitors.
Weak/Strong dance ++;
Break up ternary for legibility.
Don't blanket remove ourselves as an observer.
Block style fix.
Check the popover is still transient before closing.
Another weak/strong dance.
Copy the transientEventMonitors.
Close the popover window on dealloc of the popover.
Merge pull request #93 from github/fix-popover-transient-behaviour

Add semi-transient and fix transient popover behaviours