Improved docs with custom logo and favicon

lib/runtime/src/cache.rs

@@ -173,5 +173,4 @@ mod tests {
         // verify it works
         assert_eq!(value, 43);
     }
-
 }

lib/runtime/src/lib.rs

@@ -7,6 +7,9 @@
     unused_unsafe,
     unreachable_patterns
 )]
+#![doc(html_favicon_url = "https://wasmer.io/static/icons/favicon.ico")]
+#![doc(html_logo_url = "https://avatars3.githubusercontent.com/u/44205449?s=200&v=4")]
+
 //! Wasmer-runtime is a library that makes embedding WebAssembly
 //! in your application easy, efficient, and safe.
 //!