Changed the keepChannel to buffered channel.

Since the keepChannel is used to send data, not just for synchronizaiton,
so make it a buffered channel can avoid unnecessary goroutine yields.
Merge pull request #445 from yifan-gu/buffered_chan

Changed the keepChannel to buffered channel.
adding firewall instructions to the README
Merge pull request #447 from juliaferraioli/master

Add firewall instructions to the update demo
Add link env vars.
Merge pull request #440 from brendandburns/link

Add Docker link style env vars to link containers to services.