Now the user can create and destroy IMTs at will, though currently
destroying IMTs is currently all or nothing (imt_drop_all).
An IMT is created via imt_create which takes the keydest name (key_game
etc), the name of the IMT (must be unique for all IMTs) and optionally the
name of the IMT to which the key binding search will fall back if there is
no binding in the current IMT, but must be already defined and on the same
keydest. This means that IMTs now have user determined fallback paths. The
requirements for the fallback IMT prevent loops and other weird behaviour.
Actual key binding via in_bind is unaffected. This is why the IMT name must
be unique across all IMTs.
The "imt" command works with the key_game keydest, but imt_keydest is
provided for specifying the active IMT for a specific keydest.
At startup, default IMTs are setup to emulate the previous static IMTs so
old configs will continue to work (mostly). New config files will be
written with commands to drop all of the current IMTs and build new ones,
with the bindings and active IMT set as well.
ranges can be used efficiently. move the auto-allocated builtins to
0x10000000-0x7fffffff. should be more than enough :)
use static builtin tables ("nul" terminated) instead of a series of
function calls to add builtins to a vm. should be more memory efficient.
