Add hostname(1) implementation

This isn't exactly compatible with net-tools, but it is close.

Good:

• All short-form parameters from hostname that deal with the actual node's name (-d, -f, -i, -s, -v) are implemented.
• Files can be read in with -F.
• Works on all systems I tested it on.

Bad:

• Long-form options (--domain, --fqdn, --verbose, etc) are not supported and will cause an error.
• The manpage could use a lot of work.
• Lines longer than 1,024 characters in a file aren't handled the same way as net-tools, though I sincerely hope nobody is using that behaviour.