Replaced three (logically) identical files with a single file.

libsrc/common/toascii.s

@@ -0,0 +1,10 @@
+;
+; unsigned char __fastcall__ toascii (unsigned char c);
+; /* Convert a target specific character to ascii */
+;
+
+        .export         _toascii
+
+_toascii:
+        ldx     #>$0000
+        rts