Create a new print function and use it in the print macro

This fixes the deadlock problem, because the format_args is now evaluated before locking the screen writer. So `println!("{:?}", {println!("");})` no longer triggers a deadlock.

src/vga_buffer.rs

@@ -28,11 +28,15 @@ macro_rules! println {
 
 macro_rules! print {
     ($($arg:tt)*) => ({
-            use core::fmt::Write;
+            $crate::vga_buffer::print(format_args!($($arg)*));
-            $crate::vga_buffer::WRITER.lock().write_fmt(format_args!($($arg)*)).unwrap();
     });
 }
 
+pub fn print(args: fmt::Arguments) {
+    use core::fmt::Write;
+    WRITER.lock().write_fmt(args).unwrap();
+}
+
 pub fn clear_screen() {
     for _ in 0..BUFFER_HEIGHT {
         println!("");