Filter html5ever log messages

Author: mattico

src/bin/mdbook.rs

@@ -92,6 +92,8 @@ fn init_logger() {
     } else {
         // if no RUST_LOG provided, default to logging at the Info level
         builder.filter(None, LevelFilter::Info);
+        // Filter extraneous html5ever not-implemented messages
+        builder.filter(Some("html5ever"), LevelFilter::Error);
     }
 
     builder.init();