nsh is a work in progress, diffs are welcome

Cleanup:

* Document all new commands in the manual
* Bug hunt
* More code refactoring and re-use

To be implemented: 

* umb
* handle newer bridge commands
* handle newer 802.11 gunk like rssi display, chan, flags, nodes
* ndp controls
* privsep? multiple daemons?
* Build a simple web interface that works through the rc file handler or
  via imsg/some other privsep
* copy configs from/to tftp/sftp/https/other parts of filesystem/etc
* RSA certificate generation/management method (isakmpd, iked, sshd)
* Persistent comments/remarks in the config file (to document routes, etc..)
  (this was already done for rtable descriptions, and the database could be
  used the same way for routes)
* Better support for paging through displays of text X lines at a time
* Something comparable to pipe-grep for matching output
* More context-sensitive help, the framework is extensible
* Generate example configs for BGP+MPLS, IPv6+BGP, IPv6+Link local GIF,
  vport+veb, ipsec/ike, wg, and many other interesting feature
  combinations/scenarios.

Would be nice:

* Add more diagnostic messages for verbose output where useful
* Convenient/automatic mechanisms to centralize configurations for
  tracking/revision control
  (can already be done by adding cvs/got commit calls to save.sh)

Known Bugs (or, things that I don't want to bother with right now, but
better not forget later...):

* The kernel does not keep count of information displayed in 'show rtstat'
  properly (what else??)
  (Very old, possibly no longer valid)
