Flux release v0.2

NB The main Docker image names have changed in this release: specifically, weaveworks/flux-balancer and weaveworks/flux-agent are now combined in weaveworks/fluxd, and weaveworks/flux-fluxctl is now weaveworks/fluxctl. Please update your scripts / demos / docs accordingly.

This second release makes Flux easier to deploy and operate by merging the agent and balancer into fluxd; and, refines its service model and user interfaces.

Highlights:

• Merge the balancer and agent into one binary fluxd (and one container image)
• Send heartbeat for host from fluxd, and report live hosts in fluxctl info
• fluxd: withdraw instances that fail connections, and schedule retries with a backoff
• flux web: Show each charts alongside its instance (or group), rather than all together
• fluxd: Survive restarts of etcd, rather than crashing
• Simplify the way instances are assigned addresses, making it a global setting
• Make instances that cannot be given an address visible, to help troubleshooting

Between releases, we have improved the documentation, among other
things adding a "Get Started" guide.