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_v1/00_intro.md

@@ -17,6 +17,3 @@ To move forward you'll have to pick up several new Rust concepts, such as:
 - Modules and visibility
 - Strings
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/00_intro`

book/src/03_ticket_v1/01_struct.md

@@ -137,6 +137,3 @@ let is_open = Ticket::is_open(ticket);
 The function call syntax makes it quite clear that `ticket` is being used as `self`, the first parameter of the method,
 but it's definitely more verbose. Prefer the method call syntax when possible.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/01_struct`

book/src/03_ticket_v1/02_validation.md

@@ -15,10 +15,6 @@ This means that users can create a ticket with an empty title, a suuuuuuuper lon
 a nonsensical status (e.g. "Funny").\
 We can do better than that!
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/02_validation`
-
 ## Further reading
 
 - Check out [`String`'s documentation](https://doc.rust-lang.org/std/string/struct.String.html)

book/src/03_ticket_v1/03_modules.md

@@ -113,6 +113,3 @@ Nonetheless, it can be useful in some cases, like when writing unit tests. You m
 that most of our test modules start with a `use super::*;` statement to bring all the items from the parent module
 (the one being tested) into scope.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/03_modules`

book/src/03_ticket_v1/04_visibility.md

@@ -44,6 +44,3 @@ pub struct Configuration {
 `Configuration` is public, but you can only access the `version` field from within the same crate.
 The `active` field, instead, is private and can only be accessed from within the same module or one of its submodules.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/04_visibility`

book/src/03_ticket_v1/05_encapsulation.md

@@ -56,8 +56,4 @@ Accessor methods are public methods that allow you to read the value of a privat
 Rust doesn't have a built-in way to generate accessor methods for you, like some other languages do.
 You have to write them yourself—they're just regular methods.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/05_encapsulation`
-
 [^newtype]: Or refine their type, a technique we'll explore [later on](../05_ticket_v2/15_outro.md).

book/src/03_ticket_v1/06_ownership.md

@@ -229,9 +229,5 @@ and truly understand how they work.
 Towards the end of this chapter we'll explain _why_ Rust's ownership system is designed the way it is.
 For the time being, focus on understanding the _how_. Take each compiler error as a learning opportunity!
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/06_ownership`
-
 [^refine]: This is a great mental model to start out, but it doesn't capture the _full_ picture.
 We'll refine our understanding of references [later in the course](../07_threads/06_interior_mutability.md).

book/src/03_ticket_v1/07_setters.md

@@ -107,6 +107,3 @@ ticket.set_description("New description".into());
 ticket.set_status("In Progress".into());
 ```
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/07_setters`

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!

book/src/03_ticket_v1/09_heap.md

@@ -133,10 +133,6 @@ but there is no general-purpose "API" to retrieve runtime heap usage in Rust.\
 You can, however, use a memory profiler tool (e.g. [DHAT](https://valgrind.org/docs/manual/dh-manual.html)
 or [a custom allocator](https://docs.rs/dhat/latest/dhat/)) to inspect the heap usage of your program.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/09_heap`
-
 [^empty]: `std` doesn't allocate if you create an **empty** `String` (i.e. `String::new()`).
 Heap memory will be reserved when you push data into it for the first time.
 

book/src/03_ticket_v1/10_references_in_memory.md

@@ -45,10 +45,6 @@ The same goes for `&mut String`.
 The example above should clarify one thing: not all pointers point to the heap.\
 They just point to a memory location, which _may_ be on the heap, but doesn't have to be.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/10_references_in_memory`
-
 [^fat]: [Later in the course](../04_traits/06_str_slice.md) we'll talk about **fat pointers**,
 i.e. pointers with additional metadata. As the name implies, they are larger than
 the pointers we discussed in this chapter, also known as **thin pointers**.

book/src/03_ticket_v1/11_destructor.md

@@ -165,9 +165,5 @@ They would refer to a memory location that's no longer valid: a so-called [**dan
 a close relative of [**use-after-free bugs**](https://owasp.org/www-community/vulnerabilities/Using_freed_memory).
 Rust's ownership system rules out these kinds of bugs by design.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/11_destructor`
-
 [^leak]: Rust doesn't guarantee that destructors will run. They won't, for example, if
 you explicitly choose to [leak memory](../07_threads/03_leak.md).

book/src/03_ticket_v1/12_outro.md

@@ -4,6 +4,3 @@ We've covered a lot of foundational Rust concepts in this chapter.\
 Before moving on, let's go through one last exercise to consolidate what we've learned.
 You'll have minimal guidance this time—just the exercise description and the tests to guide you.
 
-## References
-
-- The exercise for this section is located in `exercises/03_ticket_v1/12_outro`