Drop constrain() in favor of non-broken version?

[sofian]

This relates to #73.

The constrain() macro in Arduino is counter-intuitive and unsafe IMHO because when calling because eg.

constrain(1, 3, 0)

will return 3.

I created a function safeConstrain() that solves that issue but I am wondering whether we could create another function eg. clamp(). However it looks like most functions of the same kind (numpy.clip, clamp, etc.) follow the same rule as constrain() so maybe this is no big deal...