Added white border to logo and added square logo to crate

Author: mitsuhiko

artwork/logo-square.png

@@ -106,6 +106,7 @@
 //!   removed as well.  This mainly affects the quality of error reporting.
 #![allow(clippy::cognitive_complexity)]
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![doc(html_logo_url = "https://github.com/mitsuhiko/minijinja/raw/main/artwork/logo-square.png")]
 mod key;
 
 mod ast;