Changing selftest to be done with default port 5670/udp
Connection to subscriber is done only once now. Works for multiple subscribers. Fix for #168.
Fix typo in function declaration
Simplified zyre_log_connect API

- afaics we don't need the separate methods for subscribers
- I switched to using a hash table for efficiency
- I removed the disconnect method, which was not orthogonal to
  connect, and doesn't solve any identified problem afaics
- some compile warnings removed along the way