message: Get better type errors for `impl_template`
diff: @@ -13,7 +13,8 @@ macro_rules! impl_webpage {
  ($page:ty = $template:expr $(, status = $status:expr)? $(, content_type = $content_type:expr)? $(,)?) => {
  impl $crate::web::page::WebPage for $page {
  fn template(&self) -> ::std::borrow::Cow<'static, str> {
  - $template(self)
  + let template: fn(&Self) -> ::std::borrow::Cow<'static, str> = $template;
  + template(self)
  }
  $(
  