AsyncRead: Some issues with default error type having lifetime.

[cheako]

The easy part to fix is to add some documentation about nom-bufreader, if you want an issue to track this it's #810 Some work in nom would be nice regarding https://github.com/rust-bakery/nom-bufreader/issues/9 It seems there is reason to add .to_owned() or something to nom's error type. I've been forcing () in for E, as in IResult<&[u8], Self, ()>.