Changes to keymap

I'm going to remove the theoretical, non-working keybinds for now, and
change the Build keys to those suggested by zeffii, with one exception:
I'd really like to impact default ST as little as possible, and given
that BKSPC is used for back-deleting, and we've already taken ENTER for
Run and Init, it seems like a better idea to default to CTRL+ALT+ENTER
for Kill.