add separator widget

lib/ugui.c3l/src/widgets/ugui_separator.c3

@@ -0,0 +1,16 @@
+module ugui;
+
+
+macro Ctx.separator(&ctx, int width, int height, ...)
+	=> ctx.separator_id(@compute_id($vasplat), width, height);
+fn void? Ctx.separator_id(&ctx, Id id, int width, int height)
+{
+	id = ctx.gen_id(id)!;
+	Elem *parent = ctx.get_parent()!;
+	Elem *elem = ctx.get_elem(id, ETYPE_NONE)!;
+
+	elem.layout.w = @exact((short)width);
+	elem.layout.h = @exact((short)height);
+
+	update_parent_size(elem, parent);
+}