Auto-assigned port number
-------------------------
I was a little surprised that this was not supported, I guess most torrent
client determine their port number and only then set up the DHT.
Nonethess less I think this is an interesting feature to have.
Merge pull request #11 from nhelke/auto_assign_port

Auto-assigned port number
expvar accounting for read and written UDP bytes
totalWriteBytes->totalWrittenBytes, +gofmt
Export maxInfoHashPeers and maxInfoHashes
Make MaxInfoHash.* variables instead of constants
Missing type conversion
Use less memory per server.

The network packet buffer needed ~2MB, which is un-necessary.
Fix the expvar for reachable nodes.

Export a real count of how many nodes in the routing table are
reachable. Do it opportunistically when the routing table is
being saved to disk.

Use a different expvar name because semantics are different.
Multi-node support for reachableNodes
Add back the overall count of nodes ever reached.

It's also useful by itself - specially on tests.
Better comments for routing_table.go expvars.x
Rename totalReachableNodes to totalNodesReached.
Skip certain tests when short test mode is enabled.

This helps integrating with drone.io for continuous build status.
drone.io build status badge.
Add links to the standalone find_infohash_and_wait example.
Use port 0, now supported thanks to nhelke
Fix typo in README.md
Update README.md
Update README.md