Implemented Reply for a infallible result

[comath]

http::Error implements From<Infallible>, this just shortcuts that so we can have an easy time with infallible results.

Another option is to implement the following:

impl<T,E> Reply for Result<T, E>
where
    T: Reply + Send,
    E: Reply + Send,
{ ... }

[kaj]

For reference: The "other option", impl Reply for Result<T, E> where T: Reply, E: Reply, is suggested in #458 .

[comath]

For reference: The "other option", impl Reply for Result<T, E> where T: Reply, E: Reply, is suggested in #458 .

I should have looked around some more, sorry :). I thought it'd be much much more complicated than this simple addition.