Several extensions trigger custom actions. Make sure, those actions are
only performed, if airline is actually active and not temporarily
disabled using e.g. :AirlineToggle
A new variable named cursormode_mode_func is used to store the function
returning the current mode. This allows more customization in the mapping.
The default value is the built-in mode function so there is no change in
behavior.
Add some documentation.
Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>
