RCs, Dev builds, and nightlies

There is interest from the community in having builds for:
- RCs
- dev builds (somewhere between a nightly and an RC)
- nightlies

dist.ipfs.io could show nightlies/dev builds, either:
1. as a different "distribution" (`go-ipfs-dev`), this is easiest to do
2. as an option under each distribution (we'd have to choose whether to do a grid too, and whatnot), or a "channel" (ie chose from `{release, RCs, dev, nightly}`). It will take some design work and dev work to come up with ideas on how this should look, and then implement it.
- I think (1) is easiest for go-ipfs in the short term. we could have: `go-ipfs-rc`, `go-ipfs-dev` and `go-ipfs-nightly` as distributions.
- I think (2) may be the best in the long run, particularly because other distributions will want this type of functionality. Will need to decide:
- How should channels be represented?
- as another dir in the hierarchy? (`///`)
- or as a symlink (it's really a branch, right...)? (`/ -> /`)
- or as link values in the `dist.json` (`{ ... "channels": { "": "", "release": "0.4.2", "RCs": "0.4.3-rc3", ...} }`)
- How should channels show up on the index page? maybe "tabs"? on top of the grid?
- **For now, let's first decide: (1) or (2) in the short term?**
- And then kick off work on (2).