Update the VGA buffer post for the second edition

src/main.rs

@@ -1,29 +1,29 @@
 #![feature(lang_items)] // required for defining the panic handler
+#![feature(const_fn)] // allow declaring functions as const
 #![no_std] // don't link the Rust standard library
 #![no_main] // disable all Rust-level entry points
 
-//extern crate rlibc;
+extern crate volatile;
+extern crate rlibc;
+extern crate spin;
+#[macro_use]
+extern crate lazy_static;
 
-static HELLO: &[u8] = b"Hello World!";
+#[macro_use]
+mod vga_buffer;
 
+/// This function is the entry point, since the linker looks for a function
+/// named `_start_` by default.
 #[no_mangle] // don't mangle the name of this function
 pub fn _start() -> ! {
-    // this function is the entry point, since the linker looks for a function
-    // named `_start_` by default
-    let vga_buffer = 0xb8000 as *const u8 as *mut u8;
-
-    for (i, &byte) in HELLO.iter().enumerate() {
-        unsafe {
-            *vga_buffer.offset(i as isize * 2) = byte;
-            *vga_buffer.offset(i as isize * 2 + 1) = 0xb;
-        }
-    }
+    println!("Hello World{}", "!");
 
     loop {}
 }
 
-#[lang = "panic_fmt"] // define a function that should be called on panic
-#[no_mangle] // TODO required?
+/// This function is called on panic.
+#[lang = "panic_fmt"]
+#[no_mangle]
 pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
                                _file: &'static str,
                                _line: u32,