Aullar: Add Buffer.replace
Aullar: Make Cursor.blink_interval a property

Setting it to zero disables the blink, other values
update the interval right away.
Make Cursor available from the aullar module
Aullar styles: Support aliases and add define_default
Aullar: Add Styling.reverse
Add Styling.at_pos
Add View#listener

And notify for focus events.