- Move Element.attributes to `AttrMap`, slowly using rxml's features and
unrolling our own.
- Add Element::attr_ns that requires the attribute namespace.
Element:attr defaults to rxml::Namespace::none() but the interface
changes nonetheless for a &NcNameStr. Similar changes on
`ElementBuilder` methods.
- Remove iterator structs for attributes, return a ref on the AttrMap
directly as we don't need to keep attributes' internals hidden
anymore.
- Enable rxml's `macros` feature within tests to access the `xml_ncname`
macro.
Signed-off-by: pep <pep@bouah.net>
