Improve Power (^) Scanning / Add X_SQRT()

- ignore all white space characters when seaching for the base or exponent
  in get_local_exp_part()

- add square root (X_SQRT()) to the available Excel methods

Reasons For Changes
----------------------------------------------
I came across a formula that was not evaluating properly 
```
=(0.66*M2*(P2^4)*Q2*1/$H$3^2)*(SQRT(1+0.78*(($H$3*Q2/P2^2)^2))-1)
```
`P2^4` and `P2^2` were not finding the BASE of the Power function, however `($H$3*Q2/P2^2)^2` was finding the BASE.  It seemed that only if the BASE was surrounded by parentheses [ ( ) ] would `get_local_exp_part()` find it.  

The function `get_local_exp_part()` seemed to run after the Excel formula was mostly expanded, so when not surrounded by parentheses [ ( ) ] the BASE of the Power function was on the previous line.  In order to find the BASE, `get_local_exp_part()` needed to ignore NEWLINE characters.

`X_SQRT()` is self explanatory.