Add support for relative midi knob bindings
When enabled takes the delta of the knob movement and increases/decreases the assigned convar instead of mapping it in a 0-1 range
The minimum value of the binding is used as the speed multiplier
Can be enabled when adding a binding by adding true to the end of the binding (eg."midiconvar.bindknob 1 1 graphics.dof_focus_dist 0.1 0 true")
Will only work on float convars