Add variable pulling velocity

[pfjarschel]

Change pulling velocity depending on certain conditions, such as:

• [x] Always maintain proportion relative to brusher velocity
• [x] Stop pulling in HZ edges
• [ ] Decrease pulling velocity if HZ is too long

[pfjarschel]

Stop pulling at HZ edges can be done, but not sure it would bring much benefits from it. The other aspects are simply not possible with ThorLabs motors.

[pfjarschel]

After careful testing, it seems that the procedure of stopping the puller motors, changing velocity and resuming movement is not as bad as it first seemed. Praise be the brushless motors!

[pfjarschel]

The only thing that is actually unfeasible is to maintain the velocity proportion all the time, since it would mean stopping at every loop iteration.

[pfjarschel]

Stop pulling at edges done in c2158a2c280045e2a8bfeead9d5d1ab97d425b3c, still a work in progress, as there are some bugs (#43).