anchor.diff:  }).
   
   -record(req, {
  -          method :: 'OPTIONS' | 'GET' | 'HEAD' | 'POST' |
  -                    'PUT' | 'DELETE' | 'TRACE',
  +          method :: http_method(),
             path :: [binary()],
  -          args,
  +          args :: [{binary(), any()}],
             raw_path :: binary(),
  -          version,
  +          version :: version(),
             headers :: headers(),
             body :: body(),
             pid :: pid(),
  
positive.code: 
  -type callback_mod() :: atom.
  -type callback_args() :: any().
  -type callback() :: {callback_mod(), callback_args()}.
  
  
negative.code: -type headers() :: [header()].
  -type body() :: binary() | iolist().
  -type response() :: iolist().
  -type http_method() :: 'OPTIONS' | 'GET' | 'HEAD' | 'POST' |
                         'PUT' | 'DELETE' | 'TRACE'.
  -type response_code() :: 100..999.
  -type connection_token_atom() :: keep_alive | close.
  
  -define(l2i(L), list_to_integer(L)).
  