This fixes the annoying persistence of inputs when respawning and
changing levels. Axis input clearing is hooked up but does nothing as of
yet. Active device input clearing has always been hooked up, but also
does nothing in the evdev and x11 drivers.
The listener is invoked when the axis value changes due to IN_UpdateAxis
or IN_ClampAxis updating the axis. This does mean the listener
invocation make be somewhat delayed. I am a tad uncertain about this
design thus it being a separate commit.
Each axis binding has its own recipe (meaning the same input axis can be
interpreted differently for each binding)
Recipes are specified with field=value pairs after the axis name.
Valid fields are minzone, maxzone, deadzone, curve and scale, with
deadzone doubling as a balanced/unbalanced flag.
The default recipe has no zones, is balanced, and curve and scale are 1.
