Customizable Pinion Puller

Very simple customizable gear puller mainly for small motors.

#####Non-printed parts needed
* bolt + nut (default M4)
* something to push motor axis - I'm using very small hex key bit

#####Parameters
* `hole_d` = diameter of the hole for motor axis
* `space_x`, `space_z` = size of inner room (`space_x * space_x * space_z`)
* `grip_t` = thickness of the side gripping the gear
* `side_t` = thickness of the side walls
* `nut_d` = size of the nut measured across the angles of hexagon (default is fitting M4)
* `bolt_d` = hole for bolt (it should go through freely)
* `pusher_d`, `pusher_fn` = hole for pushing part - I'm using hex key bits so `d` is size of the bit across the angles and `fn = 6` to get hexagonal hole
* `joint_h` = height of the joining part
* `joint_minimal_t` = minimal wall thickness of joining part