remap Tab to C-w and C-p to C-i (which equals Tab)

unfortunately C-i and Tab apparently have the same ASCII code and are
indistinguishable by the time they get to vim, and while I do use C-i as
the opposite of C-o, I use it way less often than C-w for switching
between split windows, and C-p by itself apparently doesn't do anything
and is right next to C-o, so.