Add RTRIM test

Author: boriel

tests/runtime/cases/rtrim_test.bas

@@ -0,0 +1,21 @@
+#include "lib/tst_framework.bas"
+
+INIT("Test RTRIM$()")
+
+#include <string.bas>
+#include <alloc.bas>
+
+print memavail; chr$(13); maxavail
+
+print "'"; rtrim("", "a"); "'"
+print "'"; rtrim("hello world", ""); "'"
+print "'"; rtrim("hello world", "ld"); "'"
+print "'"; rtrim("hello worldld", "ld"); "'"
+print "'"; rtrim("hehehe", "he"); "'"
+print "'"; rtrim("hhh", "h"); "'"
+print "'"; rtrim("ahehehe", "he"); "'"
+
+print memavail; chr$(13); maxavail
+
+FINISH
+