added docs for response headers

added explanations on current state of response headers
Merge pull request #92 from pkit/doc

added docs for response headers
doc/response: wrap short lines as paragraphs

Instead of hard line-breaks, the text now flows in paragraphs. This
makes it more natural to read.
doc/response: put examples into real literal blocks

This gives them a little more whitespace in the GitHub theme and
ensures that the line won't wrap in weird places.
doc/response: small copy editing
Merge pull request #93 from mgeisler/response

Response updates