Optimize display clearing

Author: bugadani

src/mode/buffered_graphics.rs

@@ -71,8 +71,12 @@ where
     /// Clear the display buffer. You need to call `disp.flush()` for any effect on the screen
     #[cfg(not(feature = "graphics"))]
     pub fn clear(&mut self) {
+        self.clear_impl(false);
+    }
+
+    fn clear_impl(&mut self, value: bool) {
         for b in self.mode.buffer.as_mut() {
-            *b = 0;
+            *b = value as u8;
         }
 
         let (width, height) = self.dimensions();
@@ -226,6 +230,11 @@ where
 
         Ok(())
     }
+
+    fn clear(&mut self, color: Self::Color) -> Result<(), Self::Error> {
+        self.clear_impl(color.is_on());
+        Ok(())
+    }
 }
 
 #[cfg(feature = "graphics")]