remove `impl<E> From<E> for Error where E: StdError + Send + Sync + 'static`

This might a bit controversial but I'd like to bring it up. I want to suggest to remove the generic `From`.

The reason being the following:

As long as this generic implementation exists it is not possible for errors as defined by users of this library to implement their own `Into` implementations, this makes it hard to use when you need non-generic 500 error codes.