with_* fixes

* Fix empty-but-existing query ("?") parsing bug
* Fix `with_userinfo` against hostless URI representation bug
* Fix `with_port` against hostless URI representation bug
* Fix `with_path` with relative path against hosted URI representation bug (#51)
* Fix `make` without host but with userinfo or port representation bug
* Fix `make` with host, userinfo, or port and relative path representation bug