Audit cp(1)

1) Refactor the manpage, which has been a bloody mess, documenting
   fantasy-flags (-d for example) and add a STANDARDS section
2) fix usage()
3) sort ARG-block
4) Check return-value of stat() separately, so a lack of permissions
   doesn't tell the user "the directory doesn't exist", which could
   be a bit confusing.
5) Add empty line before return.

README

@@ -20,7 +20,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
 =*  cmp             yes                          none
 #*  cols            non-posix                    none
 =*  comm            yes                          none
-=   cp              yes                          none (-i)
+=*| cp              yes                          none (-i)
 =*  cron            non-posix                    none
 #*  cut             yes                          none
 =*| date            yes                          none