IsSetAnd: Assign value depending on array entry conditions

This class can be used to assign value depending on array entry conditions.

It can check the value of an array entry and test one of several possible conditions.

The class returns the entry value if condition is satisfied, otherwise it returns NULL.

Currently it supports test conditions to verify if the array entry is set, is equal or different from another value, is a string with certain types of characters, is an array, compare with numeric values, etc..