Enable adding Model associations directly on Model definition.

Example:

var Product = db.define("product", {
    ...
});
var Sale = db.define("sale", {
    product: Product,
    ...
});

That property is the same as doing this association:

Sale.hasOne("product", Product);

lib/orm.js

@@ -491,6 +491,9 @@ ORM.prototype.define = function (model, fields, colParams) {
 				fields[k] = { "type": typeof fields[k]() };
 			} else if (o instanceof Date) {
 				fields[k] = { "type": "date" };
+			} else if (fields[k]._ORM) {
+				Model.hasOne(k, fields[k], { autoFetch: true });
+				delete fields[k];
 			} else {
 				fields[k] = { "type": fields[k] };
 			}