Reorder material on first two days (#913)

- Morning of Day 1 still introduces the language and its high-level
goals/value proposition, and starts with the built-in data types Rust
provides, and how you define a function. 
- Afternoon of Day 1 gets a front loading of the basic control flow
structures in Rust but not the more exotic ones.
- The exercises for day 1 afternoon will be the Luhn algorithm (where we
can match on digits and enums such as `Option`.
- Morning of day 2 still has discussion of memory management.

Fixes #510.

---------

Co-authored-by: Martin Geisler <mgeisler@google.com>

src/exercises/Cargo.toml

@@ -8,30 +8,30 @@ publish = false
 name = "for-loops"
 path = "day-1/for-loops.rs"
 
-[[bin]]
-name = "book-library"
-path = "day-1/book-library.rs"
-
-[[bin]]
-name = "points-polygons"
-path = "day-2/points-polygons.rs"
-
 [[bin]]
 name = "luhn"
-path = "day-2/luhn.rs"
+path = "day-1/luhn.rs"
+
+[[bin]]
+name = "book-library"
+path = "day-2/book-library.rs"
 
 [[bin]]
 name = "strings-iterators"
 path = "day-2/strings-iterators.rs"
 
-[[bin]]
-name = "safe-ffi-wrapper"
-path = "day-3/safe-ffi-wrapper.rs"
-
 [[bin]]
 name = "simple-gui"
 path = "day-3/simple-gui.rs"
 
+[[bin]]
+name = "points-polygons"
+path = "day-3/points-polygons.rs"
+
+[[bin]]
+name = "safe-ffi-wrapper"
+path = "day-3/safe-ffi-wrapper.rs"
+
 [[bin]]
 name = "dining-philosophers"
 path = "concurrency/dining-philosophers.rs"

src/exercises/day-1/afternoon.md

@@ -2,9 +2,9 @@
 
 We will look at two things:
 
-* A small book library,
+* The Luhn algorithm,
 
-* Iterators and ownership (hard).
+* An exercise on pattern matching.
 
 <details>
 

src/exercises/day-1/solutions-afternoon.md

@@ -1,9 +1,13 @@
 # Day 1 Afternoon Exercises
 
-## Designing a Library
+## Luhn Algorithm
 
-([back to exercise](book-library.md))
+([back to exercise](luhn.md))
 
 ```rust
-{{#include book-library.rs}}
+{{#include luhn.rs}}
 ```
+
+## Pattern matching
+
+TBD.

src/exercises/day-2/solutions-afternoon.md

@@ -1,13 +1,5 @@
 # Day 2 Afternoon Exercises
 
-## Luhn Algorithm
-
-([back to exercise](luhn.md))
-
-```rust
-{{#include luhn.rs}}
-```
-
 ## Strings and Iterators
 
 ([back to exercise](strings-iterators.md))

src/exercises/day-2/solutions-morning.md

@@ -1,9 +1,9 @@
 # Day 2 Morning Exercises
 
-## Points and Polygons
+## Designing a Library
 
-([back to exercise](points-polygons.md))
+([back to exercise](book-library.md))
 
 ```rust
-{{#include points-polygons.rs}}
+{{#include book-library.rs}}
 ```

src/exercises/day-3/morning.md

@@ -1,6 +1,8 @@
 # Day 3: Morning Exercises
 
-We will design a classical GUI library traits and trait objects.
+We will design a classical GUI library using traits and trait objects.
+
+We will also look at enum dispatch with an exercise involving points and polygons.
 
 <details>
 

src/exercises/day-3/solutions-morning.md

@@ -7,3 +7,11 @@
 ```rust
 {{#include simple-gui.rs}}
 ```
+
+## Points and Polygons
+
+([back to exercise](points-polygons.md))
+
+```rust
+{{#include points-polygons.rs}}
+```