rewrite: add optional cookie_rewriter, created by urlrewriter and called from header_rewriter
cookie_rewriter works correctly with a concatenated set-cookie list, returns a list of rewritten 'set-cookie' headers
rewrite_live: add proxying of Host, Origin, additional headers
split header rewriter tests into test_header_rewriter, add test_cookie_rewriter
bump version to 0.4.0!