Add free for maps (a previous oversight)

core/strings.odin

@@ -1,3 +1,5 @@
+import "mem.odin";
+
 new_string :: proc(s: string) -> string {
 	c := make([]u8, len(s)+1);
 	copy(c, []u8(s));
@@ -15,5 +17,5 @@ new_c_string :: proc(s: string) -> ^u8 {
 to_odin_string :: proc(c: ^u8) -> string {
 	len := 0;
 	for (c+len)^ != 0 do len++;
-	return string(slice_ptr(c, len));
+	return string(mem.slice_ptr(c, len));
 }