String() method: added wrapper with brackets, so it renders "( ..... AND ..... )" and now it supports nested AND/OR clauses
Values() method: fixed wrong fetching of the values (adding nil values into array of interfaces, when they are not defined), so it can supports nested AND/OR clauses
String() method: added wrapper with brackets, so it renders "( ..... AND ..... )" and now it supports nested AND/OR clauses Values() method: fixed wrong fetching of the values (adding nil values into array of interfaces, when they are not defined), so it can supports nested AND/OR clauses