clamp
ABSTRACT
Clamps an input to a range. The value of l should be less than or equal to the value of r
PARAMETERS
| l | the number denoting the start of the range |
| x | the number that we want to clamp |
| r | the number denoting the end of the range |
RETURN
r if x is greater than r, l if x is less than l, and otherwise x is returne
DECLARATION
func clamp(l, x, r)