Improved max/min functions, 2 new built in funtions.

`max/min improvements`
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* Now, Numbers **w/o units** and numbers **with units** are `compatible`. //max(0, -2px) -> 0
* First enter basis preference. max(0, -2px) //0 gets a px unit. (Which will not be reflected).

`zero :`
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It takes a dimensional value (2px, 56%, 7em, ...) as parameter and 
truncates **0unit** to only **0** while rest values remain unaltered.

**Example: zero(0em) // 0  | zero(2px) // 2px | zero(5%) // 5% | zero(0%) // 0**

`unitonly :`
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It takes a dimensional value (2px, 56%, 7em, ...) as parameter and 
returns the **unit** of the value passed.

**Example: unitonly(2px) // px  | unitonly(2em) // em | unitonly(2%) // %**