Add print! and println! macros and a clear_screen function

src/vga_buffer.rs

@@ -123,3 +123,22 @@ impl fmt::Write for Writer {
         Ok(())
     }
 }
+
+macro_rules! print {
+    ($($arg:tt)*) => ({
+        use core::fmt::Write;
+        let mut writer = $crate::vga_buffer::WRITER.lock();
+        writer.write_fmt(format_args!($($arg)*)).unwrap();
+    });
+}
+
+macro_rules! println {
+    ($fmt:expr) => (print!(concat!($fmt, "\n")));
+    ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
+}
+
+pub fn clear_screen() {
+    for _ in 0..BUFFER_HEIGHT {
+        println!("");
+    }
+}