Bug with Validate Field function

I was working with some form validation on a public facing site and noticed that the current validationEngine code does not properly validate single input fields in a form. The bug was discovered as an issue of "re-scoping".

Within the else block of the methods._validate() function, the valid variable was being rescoped and edited within. However, the variable assignment would not transcend up to the global function variables (see Line 106). As such, I removed the "re-scoping" and added a return !valid because the value of valid after Lines 140-144 is inverted. We need to properly return True for Valid and False for Invalid.