Add functionality to copy feed and append to it.

[benjaminettori]

No description provided.

[benjaminettori]

@flyingzumwalt It seems node did not start supporting promises natively until v 0.11, which means the build for v 0.10 fails. Is this an issue?

[flyingzumwalt]

@benjaminettori I think it's fine for us to only support node 0.11 and higher. Remove 0.10 from the travis.yml and update the Readme to call out the dependency on node >= 0.11.

[mafintosh]

this might append blocks in the wrong order as this is async. you probably wanna do this

loop(null)
function loop (err) {
  if (err) return reject(err)
  refFeed.get(newFeed.blocks, function (err, block) {
    if (err) return cb(err)
    if (!block) return resolve() // done
    newFeed.append(block, loop)
  })
}

[flyingzumwalt]

@mafintosh you commented in irc that you're not a fan of promises for server-side code. Could you elaborate? I think @benjaminettori chose to use promises because it was a clearer way to handle nested callbacks. @benjaminettori could you provide an example of a place where the code would get confusing without promises?

[benjaminettori]

@flyingzumwalt Actually I may have a way to do this without promises, I will submit another PR if I finalize it. I was using promises because I wanted to return a feed object, but this is probably not the best way to approach the issue. Thanks @mafintosh for catching that mistake and for the clever code snippet.

[benjaminettori]

@flyingzumwalt I refactored the code and added methods to replicate and append to feeds without using promises. I also added some tests around these new methods.