message: updated api to allow simple saving handler
diff: @@ -18,8 +18,8 @@ export interface FieldOptions<entityType = any, valueType = any> {
  caption?: string;
  displayValue?: (entity: entityType, value: valueType) => string;
  defaultValue?: (entity: entityType) => valueType | Promise<valueType>;
  - validate?: ((entity: entityType, col: FieldRef<entityType, valueType>) => (void | Promise<void>)) | ((entity: entityType, col: FieldRef<entityType, valueType>) => (void | Promise<void>))[];
  - saving?: ((entity: entityType, col: FieldRef<entityType, valueType>) => (void | Promise<void>));
  + validate?: ((entity: entityType, col: FieldRef<entityType, valueType>) => (any | Promise<any>)) | ((entity: entityType, col: FieldRef<entityType, valueType>) => (any | Promise<any>))[];
  + saving?: ((entity: entityType, col: FieldRef<entityType, valueType>) => (any | Promise<any>));
  inputType?: string;
  allowNull?: boolean;
  