Add new function - sgn(value)

[config2000]

sgn() is a classic basic function that takes one parameter and returns it's sign according these rules:

• Returns -1 if the value passed is less than 0
• Returns +1 if the value passed is greater than 0
• Returns 0 if the value passed is 0

it's useful for 'normalising' a value (for want of a better phrase) which can then be scaled back up.

The Javascript equivalent is Math.sign()

The sgn() can be done in microScript by using this function:
sgn=function(v) (v>0)-(v<0) end