add `hackney/raw/1` function

Extract raw informations from the client context

Ex:

    3> {ok, Status, Headers, Client} =
hackney:get(<<"https://friendpaste.com">>).
    {ok,200,
        [{<<"Server">>,<<"nginx/0.7.62">>},
         {<<"Date">>,<<"Sat, 23 Nov 2013 12:27:37 GMT">>},
         {<<"Content-Type">>,<<"text/html; charset=utf-8">>},
         {<<"Transfer-Encoding">>,<<"chunked">>},
         {<<"Connection">>,<<"keep-alive">>},
         {<<"Set-Cookie">>,
          <<"FRIENDPASTE_SID=43f29a9329811c81757cb60b50c74c300b2fd87c;
expires=Sat, 0"...>>},
         {<<"Access-Control-Allow-Origin">>,<<"None">>},
         {<<"Access-Control-Allow-Credentials">>,<<"true">>},
         {<<"Access-Control-Allow-Methods">>,
          <<"POST, GET, PUT, DELETE, OPTIONS">>},
         {<<"Access-Control-Allow-Headers">>,
          <<"X-Requested-With, X-HTTP-Method-Override, Content-Type,
"...>>},
         {<<"Access-Control-Max-Age">>,<<"86400">>}],
        {client,hackney_ssl_transport,"friendpaste.com",443,netloc,
                [],
                {sslsocket,{gen_tcp,#Port<0.1986>},<0.64.0>},
                {default,{"friendpaste.com",443,hackney_ssl_transport},
                         <0.60.0>,hackney_ssl_transport},
                hackney_pool,infinity,false,5,false,nil,undefined,connected,
                on_body,nil,normal,false,false,#Fun<hackney_request.send.2>,
                waiting,4096,<<...>>,...}}
    4> hackney:raw(Client).
    {on_body,hackney_ssl_transport,
             {sslsocket,{gen_tcp,#Port<0.1986>},<0.64.0>},
             <<"3b98\r\n<!DOCTYPE html>\n<html lang=\"en\">\n<head>\n
<meta charset=\"utf-8\"/>\n    <title>Friendpaste - W"...>>}

fix #46