Hail: Remove separate hail and reply messages.

Since Hail is supposed to be decentralised, all peers should be hailing. Therefore, a peer's hail can serve the same purpose as the reply message. This also helps with some problem which occur when multiple network interfaces are available, see Issue #6

Signed-off-by: Scott Wilson <i@scottwilson.ca>
Allow broadcast address to be specified in Hail and Registrant

This is more flexible, and allows additional security by restricting to a particular subnet

Signed-off-by: Scott Wilson <i@scottwilson.ca>
Hail: Restore replying, update peer info on both receiving a hail, and on receiving a reply

This is a more complete solution to Issue 6.

Signed-off-by: Scott Wilson <i@scottwilson.ca>
Merge pull request #7 from muellmusik/rework-discovery

Rework discovery