Automatically add exercise links to sections. (#52)

We use an mdbook preprocessor to automatically generate links to the relevant exercise for each section.
We remove all existing manual links and refactor the deploy process to push the rendered book to a branch.

book/src/03_ticket_v1/08_stack.md

@@ -52,10 +52,6 @@ assert_eq!(std::mem::size_of::<u8>(), 1);
 
 1 makes sense, because a `u8` is 8 bits long, or 1 byte.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/08_stack`
-
 [^stack-overflow]: If you have nested function calls, each function pushes its data onto the stack when it's called but
 it doesn't pop it off until the innermost function returns.
 If you have too many nested function calls, you can run out of stack space—the stack is not infinite!