Add smol-rs logo (#46)

Author: notgull

src/lib.rs

@@ -19,6 +19,12 @@
 //! ```
 
 #![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
+#![doc(
+    html_favicon_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
+)]
+#![doc(
+    html_logo_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
+)]
 
 use std::cell::RefCell;
 use std::fmt;