Add missing usage and getopt(3) options

• Add the missing option 'n' to the getopt(3) string
• Add the missing options 'libxo' and 'N' to the usage message
• Add the missing options 'M' and 'N' to the man-page

Submitted by: Keegan Drake H.P. <kdrakehp@zoho.com>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D10915