[WIP] Refacto 3.0

This is a refactor of Elephant.IO. At a first pass, it will support only emitting data, leaving the reading / keeping alive parts as stubs to be filled for later.

It should support Socket.IO 0.9 and 1.0.

right now, it won't support (yet) namespaces (such as proposed by #28), callbacks (implemented in 2.0 by #39), or reading from the socket, even though there is a stub waiting to be completed just for that.

I also plan to use most of the Payload's version proposed in #49.

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- [x] Break up the Payload class
- [x] Adapt tests from the old Payload class
- [x] Make the client a wrapper
- [ ] Socket.io 0.x engine implementation
- [ ] Socket.io 1.x engine implementation
- [ ] Tests for the Socket.io implementations
seems legit. Done in 7070dd7