proposal: add new field property `Order` to check field monotonicity

[wenchy]

enum Order {
    ORDER_NONE = 0;
    ORDER_INCR = 1; // increasing
    ORDER_DECR = 2; // decreasing
}

Example

Score	Desc
Map<int32, Item>|{order:ORDER_INCR }	string
Item's score	Item's desc
1	desc1
5	desc5
8	desc8