Assignmentexpression support

support on AssignmentExpression
1. add option to multiple declare variable
2. update type of an object if needed when assignment takes place 
   example: var a = "a" ; 
                  a  =3 ;
than type of a will be number
3. support on adding property to an object  or changing its type
   example var a = {id:1};
                a.name = "eliran"; // a now have two properties
                a.id = "id1"; //a.id type is now number
4. also added tests folder for expressions