Use a more push-based approach to handle async case.

[stevefan1999-personal]

Judging from the discussion on #13, it seems like adding async support would be a PITA because 1. maintenance hell with two copies of almost the same thing and 2. there is no standard regarding async and the use of io::Error in no_std situation which makes it very painful to write for in the first place.

I guess its time that we should discuss for a more modular, push-based approach similar to httparse. Then the user should handle the read write outside of the stream accordingly.

This of course means the responsibility would be offloaded to user and it will be a major semver break situation.

[stevefan1999-personal]

Another way of reliving this is use poll_ style...I'm still learning about this matter though.