Add and use a clear_screen function

src/lib.rs

@@ -25,6 +25,7 @@ mod vga_buffer;
 #[no_mangle]
 pub extern fn rust_main() {
     // ATTENTION: we have a very small stack and no guard page
+    vga_buffer::clear_screen();
     println!("Hello World{}", "!");
 
     loop{}

src/vga_buffer.rs

@@ -23,6 +23,12 @@ macro_rules! print {
     });
 }
 
+pub fn clear_screen() {
+    for _ in 0..BUFFER_HEIGHT {
+        println!("");
+    }
+}
+
 #[allow(dead_code)]
 #[repr(u8)]
 pub enum Color {