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/tests/parsing.rs

@@ -0,0 +1,21 @@
+use leon::{Item, Template};
+
+#[test]
+fn test() {
+    assert_eq!(leon_macros::template!(""), Template::new(&[], None),);
+
+    assert_eq!(
+        leon_macros::template!("a"),
+        Template::new(&[Item::Text("a")], None),
+    );
+
+    assert_eq!(
+        leon_macros::template!("{1}"),
+        Template::new(&[Item::Key("1")], None),
+    );
+
+    assert_eq!(
+        leon_macros::template!("a{ 1 } c"),
+        Template::new(&[Item::Text("a"), Item::Key("1"), Item::Text(" c")], None),
+    );
+}