add `hackney_url:normalize/1`

normalize the encoding of an url.

Ex:
<<"http://www.è©¹å§æ¯.com/atomtests/iri/è©¹.html"/utf8>>
1> Url = <<"http://www.è©æ¯.com/atomtests/iri/è©¹.html"/u,
1> hackney_url:unparse_url(hackney_url:normalize(V))
<<"http://www.xn--8ws00zhy3a.com/atomtests/iri/%e8%a9%b9.html">>