Render the book in PDF using pandoc and LaTeX. (#126)

* Render the book in PDF using `pandoc` and LaTeX.

* Fix installs.

* Go the apt-get route

* Another attempt

* Avoid installing twice.

* Re-order.

* Add more packages.

* Minimise deps. Fix link checker.

* Missing package.

* Missing package.

* Missing package.

* More packages.

* Missing package.

* Missing package.

* More packages...

* Remove.

* Fix link checker.

* Fix link checker.

* Fix path.

* Add subtitle.

* Avoid running over the right margin.

* Avoid running over the right margin.

* Formatting

book/src/08_futures/04_future.md

@@ -55,7 +55,8 @@ note: future is not `Send` as this value is used across an await
     |         -------- has type `Rc<i32>` which is not `Send`
 12  |     // A `.await` point
 13  |     yield_now().await;
-    |                 ^^^^^ await occurs here, with `non_send` maybe used later
+    |                 ^^^^^ 
+    |   await occurs here, with `non_send` maybe used later
 note: required by a bound in `tokio::spawn`
     |
 164 |     pub fn spawn<F>(future: F) -> JoinHandle<F::Output>
@@ -84,7 +85,10 @@ trait Future {
     type Output;
     
     // Ignore `Pin` and `Context` for now
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
+    fn poll(
+      self: Pin<&mut Self>, 
+      cx: &mut Context<'_>
+    ) -> Poll<Self::Output>;
 }
 ```