Move the mention of viewing usage info via 'nethack --usage | more'
to the end, where it should remain visible if text has scrolled off
the top of the screen (which is nearly certain since it ended up
being much longer than originally intended).
Also, rephrase the text at the start about restore vs new game since
the previous description said "in all cases" which isn't applicable
for 'nethack --scores' or --version or --showpaths or --usage.
Move 'nethack --usage' to last so that 'nethack --scores' is first
among the non-playing command variants since -s is of more interest.
For 'nethack --scores', move -v before the other options since it
has to be next after -s|--scores to be processed correctly. Also,
avoid using "present" twice in the same sentence.
Instead of using a compile-time macro to suppress inclusion of the
menu entry to show UNIX command-line usage in the help menu, use a
sysconf setting instead.
Default is HIDEUSAGE=0, to include the entry for command-line usage.
Set HIDEUSAGE=1 to exclude that. Does not affect 'nethack --usage'
if player actually has access to the command-line.
Write up a description of how the command line works on UNIX and put
that in new file dat/usagehlp. Add support for
|nethack --usage | --help | -? | ?
to display it and exit.
Also add a menu entry for nethack's help command to show it during
play. That can be suppressed by uncommenting new '#define HIDE_USAGE'
in config.h since it won't be useful on servers that don't give
players access to command lines.
New genl_display_file() just writes to stdout. opt_usage(), which
calls it, might need some suid/sgid handling to make sure the output
is done as the player rather than as nethack.
doc/nethack.6 is already out of date again.
