- Change the way that the response headers are reconstructed to reduce
  the chance of memory being incorrectly allocated.
- Return the correct error when a header is not found.
- remove all the response headers before receiving new ones so that we
  don't merge headers from two responses.
- Add extra standard fields.
- Split the status line into http version, status code and status text
  and store those in the response data, without using use a fake
  field.