Update rdiscd man page

Document privilege separation options.  Improve formatting.
Improve wording in rdiscd man page
Improve rdiscd man page formatting

Ensure rdiscd is always in bold, per convention.
Clarify a comment
Reference RFC 7217 instead of draft stable privacy standard
Fix typos in the documentation

Introduced by previous commit, 93ac261cbb95b73b208d31c1919bb8c3079acb5f.
Disallow empty interface names

They're bound to cause problems later.
Fix a typo in a comment
Factor out RFC 7217 code into common file
Add rdiscd-mkaddress, a tool for generating an IPv6 address

It uses the same logic to generate an addresses as rdiscd, and takes
similar command line arguments.

Example usage to generate a stable privacy address for a host on the
given prefix with the given MAC address:

	rdiscd-mkaddress -k /etc/rdiscd.key -m 00:53:12:92:f3:9a 2001:db8:92e:b51f::/64 stable-privacy
rdiscd-mkaddress: improve the wording of usage message
Add NEWS file, release 0.5
ifupdown hook: read config value from file if value prefixed with '<'

For example, to configure eth0 using a static interface ID that is read
from /etc/eth0-interface-id:

	iface eth0 inet6 manual
		rdiscd yes
		rdiscd-interface-id </etc/eth0-interface-id
Merge tag '0.5' into debian

Release 0.5
Clean up / modernize Debian packaging

 * Remove pointless Build-Depends
 * Upgrade to modern copyright file format
 * Switch to quilt source format
 * Use pristine-tar
debian packaging: refer to RFC 7217 in description
debian packaging: also install rdiscd-mkaddress
debian packaging: update changelog for 0.5-1