This alt code allows one to resize the maze. Obviously if one uses -D
with a value that's not a number it will fail to compile. If it's <= 0
|| >= 5000 it will set to the default of 39.
The try.alt.sh script plays with this, first selecting a random number
(in range $RANDOM % 38) to compile with and then run. After that it runs
in an infinite loop, exiting only if input includes non-digit
characters. A value >= 5000 sets it to the default of 39 (in the code).
Updated the README.md files.
Renamed shapiro/shapiro.orig.c -> shapiro/shapiro.alt.c. This is one of
the exceptions where we have the alt version as this alt version is not
actually in the archive tarball (there are other exceptions for various
reasons).