Limit Motion Constraint

A constraint that let the user to control the way a bone or object is displaced in 3D viewport by setting a "step" distance, so you can only move the selected bone/object in discrete steps. Let's say you set a step of 0.02 Blender units, then each time you move the bone it snaps its position in 0.02 BU intervals in the indicated direction/axis. Would be useful for rig GUIs, to make controls move in discrete steps instead of continuous motion. Currently it can be done using snapping and the grid, but it is uncomfortable to switch on/off all the time.