lockf.1: Organize and provide error numbers

Add error numbers to the exit codes so that readers can decode them
without having to use a separate utility. Organize exits by error code.
Mark up the error constants with the error constant macro, even though
this is really not very helpful because people will search for the error
code, the macro is explicitly for the constants and not the codes.

While where, align and alphabetize the options list as well, fix
misaligned padding in an example, and a one-sentance-per-line error.

MFC after: 3 days
Reported by: Antranig Vartanian <antranigv@freebsd.am>
Differential Revision: https://reviews.freebsd.org/D48470