implemented NORMAL math routine, added more stubs

c64/basic/,stubs_math/b391.GIVAYF.s

@@ -0,0 +1,20 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - 16-bit signed integer to FAC1
+//
+// Output:
+// - .A - address high byte (XXX really, not the opposite?)
+// - .Y - address low byte
+//
+// See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 107
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+//
+
+// XXX provide implementation
+
+GIVAYF:
+	STUB_IMPLEMENTATION()