Add spread bool to Parameter (#83)

Author: bennypowers

schema.d.ts

@@ -592,6 +592,11 @@ export interface Parameter extends PropertyLike {
    * Whether the parameter is optional. Undefined implies non-optional.
    */
   optional?: boolean;
+  /**
+   * Whether the parameter is a rest parameter. Only the last parameter may be a rest parameter.
+   * Undefined implies single parameter.
+   */
+  rest?: boolean;
 }
 
 export interface FunctionLike {