Adding Membership Operator

Hello, Yara-X **_rule conditions_** lack a membership operator with array notation. Something like this: `pe.os_version.major in {5, 8, 10, 11, 13, 14}` It would be nice if the membership operator accepts different types, `string`, `dec`, `hex`, `char`, `float `and `double`, among others. For now, we have the function `in_range(test, lower, upper)` from the math module, which accepts a range only, and not a list of values.