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/bin/src/args.rs

@@ -31,7 +31,7 @@ use strum_macros::EnumCount;
 pub struct Args {
     /// Packages to install.
     ///
-    /// Syntax: crate[@version]
+    /// Syntax: `crate[@version]`
     ///
     /// Each value is either a crate name alone, or a crate name followed by @ and the version to
     /// install. The version syntax is as with the --version option.