Add new crate leon-macros that provide template! with identical syntax as runtime parsing (#946)

`leon_macros::template!` can parse template at compile-time.
It accepts a utf-8 string literal and uses `leon` internally to parse it, then generate code that evaluates to `Template<'static>`.

 - Exclude fuzz from crate leon when publishing
 - Impl fn-like proc-macro `leon_macros::template!`
 - Add dep `leon-macros` to binstalk
 - Use `leon_macros::template!` in `binstalk::fetchers::gh_crate_meta::hosting`
 - Add doc for `leon-macros` in `leon`
 - Improve `std::fmt::Display` impl for `leon::ParseError`
 - Fixed broken infra link in leon

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/leon-macros/src/lib.rs

@@ -0,0 +1,36 @@
+use leon::{Item, Template};
+use quote::quote;
+use syn::{parse_macro_input, LitStr};
+
+#[proc_macro]
+pub fn template(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as LitStr).value();
+
+    #[allow(clippy::unnecessary_to_owned)]
+    let items = Template::parse(&input)
+        .unwrap()
+        .items
+        .into_owned()
+        .into_iter()
+        .map(|item| match item {
+            Item::Text(text) => quote! {
+                ::leon::Item::Text(#text)
+            },
+            Item::Key(key) => quote! {
+                ::leon::Item::Key(#key)
+            },
+        });
+
+    quote! {
+        ::leon::Template::new(
+            {
+                const ITEMS: &'static [::leon::Item<'static>] = &[
+                    #(#items),*
+                ];
+                ITEMS
+            },
+            ::core::option::Option::None,
+        )
+    }
+    .into()
+}