Add a VGA buffer module skeleton

It contains basic types for colors, screen characters, and the buffer itself.

src/lib.rs

@@ -13,10 +13,13 @@
 // limitations under the License.
 
 #![feature(no_std, lang_items)]
+#![feature(const_fn)]
 #![no_std]
 
 extern crate rlibc;
 
+mod vga_buffer;
+
 #[no_mangle]
 pub extern fn rust_main() {
     // ATTENTION: we have a very small stack and no guard page

src/vga_buffer.rs

@@ -0,0 +1,39 @@
+const BUFFER_HEIGHT: usize = 25;
+const BUFFER_WIDTH: usize = 80;
+
+#[repr(u8)]
+pub enum Color {
+    Black      = 0,
+    Blue       = 1,
+    Green      = 2,
+    Cyan       = 3,
+    Red        = 4,
+    Magenta    = 5,
+    Brown      = 6,
+    LightGray  = 7,
+    DarkGray   = 8,
+    LightBlue  = 9,
+    LightGreen = 10,
+    LightCyan  = 11,
+    LightRed   = 12,
+    Pink       = 13,
+    Yellow     = 14,
+    White      = 15,
+}
+
+struct ColorCode(u8);
+
+impl ColorCode {
+    const fn new(foreground: Color, background: Color) -> ColorCode {
+        ColorCode((background as u8) << 4 | (foreground as u8))
+    }
+}
+
+struct ScreenChar {
+    ascii_character: u8,
+    color_code: ColorCode,
+}
+
+struct Buffer {
+    chars: [[ScreenChar; BUFFER_WIDTH]; BUFFER_HEIGHT],
+}