A complete refactor using promises instead of thunks with other new features and API changes.

[brentropy]

Remaining things to do before merging:

• [ ] Write tests for new code in src/ (could be based on old test that are not removed yet)
• [x] Add prepublish build step
• [x] Update dependencies, this hasn't been touched in a long time
• [ ] Update examples (use async await instead of co, with maybe one co specific example)
• [ ] Recreate async.js in the new code
• [ ] Fix bugs
• [x] Remove old code in lib/

[brentropy]

@coderhaoxin I have had some time to work on this. I will try to push up some stuff by tomorrow morning. I am updating the dependencies, writing tests, and improving the select functionality.

[brentropy]

@coderhaoxin I just pushed up a bunch of stuff, there is still more to be done, but I will try to take some time over the weekend.

Let me know if you have any feedback on what I am doing in this branch.