Implement infrastructure around new lexer

The lexer itself is very much incomplete, but this is intended to be a
safe point to revert to should further implementation go south.

include/asm/main.h

@@ -43,6 +43,10 @@ void opt_Push(void);
 void opt_Pop(void);
 void opt_Parse(char *s);
 
+void upperstring(char *s);
+void lowerstring(char *s);
+
+/* TODO: are these really needed? */
 #define YY_FATAL_ERROR fatalerror
 
 #ifdef YYLMAX