ON HOLD: Factor out the part of the follow function in stepper_controls

[Hsenrab]

Currently the follow function on the axis pair class takes a curve. It then extracts a set of points from the curve before doing the main 'follow' logic.

This logic needs to be factored out into a separate function that can be called with:

• Set of points
• Pen speed
• bool indicating whether soft limits should be used. This is so this function can be called directly in challenge 2.

The warning about homing should also be moved internally to this new function. The current function should be renamed to follow_curve and the new called follow_points. follow_curve should call follow_points internally. and the behaviour of this function remain unchanged it should have no affect on anything currently calling follow.

[Hsenrab]

Target completion date 14/03/16

[Hsenrab]

Create a new branch for this issue off the master branch.

[Hsenrab]

Putting this issue on hold. We are currently creating curves for each line segment we want to follow. This is a possible speed up if we need it,