Usage info is mangled by symbol substitution

[DavidGriffith]

For the page of info printed by Frotz when started without a zcode file to load, one can see that the word "interpreter" has been mangled to something else.

[DavidGriffith]

Pull #3 fixes the problem by adding (?!\\w) to the starting regex, which makes it ignore alphanumeric characters after the match -- so interpreter doesn't get turned into A00033er among other things.

[DavidGriffith]

There's something about sed that isn't working correctly or I don't completely understand what's going on. According to testing at https://www.regextester.com/, a regex of interpret(?!\w) should match interpret, but not interpreter. When I put it into my snavig script and your gnusto script, it didn't perform like that. Rather, it matched nothing in the Frotz source code. So, I'd like to back out this commit and go back to the drawing board.

[DavidGriffith]

Now fixed and verified in #4.