Permit PUT as an HTTP method

`HTTP::Request::Common` suggests that `PUT` is just like `GET` and `DELETE`:

    sub GET  { _simple_req('GET',  @_); }
    sub HEAD { _simple_req('HEAD', @_); }
    sub PUT  { _simple_req('PUT' , @_); }
    sub DELETE { _simple_req('DELETE', @_); }

I guess we could at `HEAD` too, but, eh, I actually need `PUT`. :)