Getting 3.0.0 released

The 3.0.0 branch has been around for a long time, and I don't think any of us ever meant to drag it out for so long. I believe much of this is due to lack of motivation by the maintainers (especially me) to push things forward and get it released.

As it is, there are people [actually using](https://github.com/caolan/highland/issues/458) the 3.0 beta release, and we are getting [requests](https://github.com/caolan/highland/issues/532#issuecomment-245044369) for new features to be forward ported to 3.0. I think it's important that we actually get the thing properly released.

To that end, I propose that we switch the `master` branch to point at 3.x code and relegate 2.x code to a bugfix branch. The hope is that this will provide some form of motivation for people to contribute to 3.x. It would also be easier to make more radical changes to 3.x (e.g., split up `index.js`) if we don't have to worry about merging in 2.x code all the time. What are peoples' thoughts? @svozza? (picking on you since you seem to be around.)

Also, if there anybody reading this who would like to help us get to a 3.0.0 release, please let me know!

Review the 3.x branch and the release-related discussions linked in the issue, starting with index.js and the current branch layout. Determine the remaining work needed to move master to 3.x, preserve 2.x bug fixes, and publish a proper 3.0.0 release.

Written by the indexing model from the issue text.