0.3.0

This is the first release under the new package name.

It mostly fixes minor bugs and issues regarding document encoding. Furthermore, it introduces additional API for manipulation of namespaces bound to Element: Element::top_parent, Element::is_quantified, Element::quantify_with_closest, Element::has_self_declared_namespace, Element::find_quantified, Element::find_all_quantified, Element::collect_namespace_prefixes, Element::collect_applicable_namespace_decls, Element::collect_external_namespace_decls, and Element::closest_prefix.