inadyn: add package for inadyn DDNS client-updater

inadyn is a DynamicDNS client/updater which works with dyndns.com, noip.com
and many other DDNS providers.  It is minimal in footprint and requirements,
supports IP caching, multiple providers, multiple domain names, and
a variety of other situations.

[Peter: fixup whitespace / trailing spaces]
Signed-off-by: Dave Purdy <david.c.purdy@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>