Add asyncio support to async portion.

[zet4]

Personally I prefer to work with asyncio when I need async instead of big and clunky tornado, so I am wondering if it would be possible to add such support to the project?

[reubano]

This uses twisted, not tornado. But i do plan on integrating asyncio in the future. Note that not all features will be easily ported since twisted supports more protocols and has many async functions builtin. At the very minimum though, I plan to add async http fetching. Feel free to submit PR with any suggestions!