Use new Unique API (#346)

Change Unique to use `new_unchecked`. Fixes #345.

blog/content/posts/04-printing-to-screen/index.md

@@ -247,7 +247,7 @@ pub fn print_something() {
     let mut writer = Writer {
         column_position: 0,
         color_code: ColorCode::new(Color::LightGreen, Color::Black),
-        buffer: unsafe { Unique::new(0xb8000 as *mut _) },
+        buffer: unsafe { Unique::new_unchecked(0xb8000 as *mut _) },
     };
 
     writer.write_byte(b'H');
@@ -431,7 +431,7 @@ To provide a global writer that can used as an interface from other modules, we
 pub static WRITER: Writer = Writer {
     column_position: 0,
     color_code: ColorCode::new(Color::LightGreen, Color::Black),
-    buffer: unsafe { Unique::new(0xb8000 as *mut _) },
+    buffer: unsafe { Unique::new_unchecked(0xb8000 as *mut _) },
 };
 ```
 
@@ -479,7 +479,7 @@ use spin::Mutex;
 pub static WRITER: Mutex<Writer> = Mutex::new(Writer {
     column_position: 0,
     color_code: ColorCode::new(Color::LightGreen, Color::Black),
-    buffer: unsafe { Unique::new(0xb8000 as *mut _) },
+    buffer: unsafe { Unique::new_unchecked(0xb8000 as *mut _) },
 });
 ```
 [Mutex::new] is a const function, too, so it can be used in statics.

blog/content/posts/06-page-tables/index.md

@@ -659,7 +659,7 @@ Because the `ActivePageTable` owns the unique recursive mapped P4 table, there m
 impl ActivePageTable {
     pub unsafe fn new() -> ActivePageTable {
         ActivePageTable {
-            p4: Unique::new(table::P4),
+            p4: Unique::new_unchecked(table::P4),
         }
     }
 }

src/memory/paging/mapper.rs

@@ -19,7 +19,7 @@ pub struct Mapper {
 
 impl Mapper {
     pub unsafe fn new() -> Mapper {
-        Mapper { p4: Unique::new(table::P4) }
+        Mapper { p4: Unique::new_unchecked(table::P4) }
     }
 
     pub fn p4(&self) -> &Table<Level4> {

src/vga_buffer.rs

@@ -18,7 +18,7 @@ const BUFFER_WIDTH: usize = 80;
 pub static WRITER: Mutex<Writer> = Mutex::new(Writer {
     column_position: 0,
     color_code: ColorCode::new(Color::LightGreen, Color::Black),
-    buffer: unsafe { Unique::new(0xb8000 as *mut _) },
+    buffer: unsafe { Unique::new_unchecked(0xb8000 as *mut _) },
 });
 
 macro_rules! println {