Use explicitly-named args in impl_render_with_display (#328)

* Use explicitly-named args in `impl_render_with_display`

Implicitly-named args were failing on Rust 1.57 (but worked on Nightly).

* Fix macro formatting

Also add a TODO comment to revert later.

Co-authored-by: Chris Wong <lambda.fairy@gmail.com>

maud/src/lib.rs

@@ -155,7 +155,8 @@ macro_rules! impl_render_with_display {
         $(
             impl Render for $ty {
                 fn render_to(&self, w: &mut String) {
-                    format_args!("{self}").render_to(w);
+                    // TODO: remove the explicit arg when Rust 1.58 is released
+                    format_args!("{self}", self = self).render_to(w);
                 }
             }
         )*