element-wise clamp

[John-Colvin]

Wouldn't it be neat to be able to write:

assert(clamp(vec2(-4.3, 2), -3, 4) == vec2(-3, 2));
assert(clamp(vec2(-2, 4), vec2(0, 0), vec2(1, 3)) == vec2(0, 3));

[Dav1dde]

I like the idea. Hopefully I have time in the next week(s) to work on all the open issues.