Until now the 'update' method used mp.command_native with a hardcoded
list of key names.
Change it to use whatever keys the user set to this object, so that
we can remain oblivious to new keys which 'osd-overlay' may support.
This is how the lua code did it from the begining. We didn't, and now
we pay the price.
Note: could be implemented either as we have now (clone `this`
excluding the methods) or by moving the methods up the prototype chain
(i.e. class methods) so they don't get enumerated and use `this` as
the command object itself.
However, in the latter approach we'll have to save the values which we
change (name, res_x, res_y) and restore them after the command, so it's
simpler to just clone `this`.
Avi Halachmi (:avih)
9cf45d8300