minidom: breaking: Allow getting Element attributes by namespace

- 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>

parsers/src/receipts.rs

@@ -35,6 +35,7 @@ mod tests {
     use crate::ns;
     use minidom::Element;
     use xso::error::{Error, FromElementError};
+    use xso::exports::rxml;
 
     #[cfg(target_pointer_width = "32")]
     #[test]
@@ -80,13 +81,13 @@ mod tests {
         let receipt = Request;
         let elem: Element = receipt.into();
         assert!(elem.is("request", ns::RECEIPTS));
-        assert_eq!(elem.attrs().count(), 0);
+        assert_eq!(elem.attrs().into_iter().count(), 0);
 
         let receipt = Received {
             id: String::from("coucou"),
         };
         let elem: Element = receipt.into();
         assert!(elem.is("received", ns::RECEIPTS));
-        assert_eq!(elem.attr("id"), Some("coucou"));
+        assert_eq!(elem.attr(rxml::xml_ncname!("id")), Some("coucou"));
     }
 }