add exercises for protocols and touch up content

.gitignore

@@ -0,0 +1 @@
+/todo

exercises/arithmetic.livemd

@@ -162,7 +162,7 @@ Ten times ten times ten.
 
 ```
 
-ten to the power of two hundred and one.
+Ten to the power of two hundred and one.
 
 ```elixir
 

exercises/bottles_of_soda.livemd

@@ -0,0 +1,95 @@
+# Bottles Of Soda
+
+## Bottles of Soda
+
+In the Elixir cell below create a module `BottlesOfSoda` with a function `on_the_wall/0`.
+See further instructions below, you should implement each step one by one on the `BottlesOfSoda` module
+
+```elixir
+
+```
+
+### Step 1
+
+`on_the_wall/0` should
+
+* From 99 to 1 return a list with the string
+
+```elixir
+"
+X bottles of soda on the wall.
+X bottles of soda.
+Take one down, pass it around.
+X - 1 bottles of soda on the wall.
+"
+```
+
+Where the `X` is the number of bottles of soda remaining.
+
+### Step 2
+
+* when X is 1, use the correct grammar:
+
+```elixir
+"
+1 bottle of soda on the wall.
+1 bottle of soda.
+Take one down, pass it around.
+0 bottles of soda on the wall.
+"
+```
+
+### Step 3
+
+* When X is 0, use the following phrase:
+
+```elixir
+"
+No more bottles of soda on the wall, no more bottles of soda.
+Go to the store and buy some more, 99 bottles of soda on the wall.
+"
+```
+
+### Step 4
+
+* Create an `on_the_wall/1` function which takes in a positive **integer** for the `number_of_bottles` of soda on the wall.
+* From `number_of_bottles` to `0`, repeat the expected song lyrics.
+
+### Step 5
+
+* Allow the `on_the_wall/1` function to also accept a descending **range** to perform the rhyme from.
+  i.e. `BottlesOfSoda.on_the_wall(99..50)`.
+
+### Step 6
+
+* Create an `on_the_wall/2` function which accepts an **integer** or a **range** for the first parameter.
+* For the second parameter, the function should accept a "string" for the type of beverage.
+
+For example `BottlesOfSoda.on_the_wall(99, "pop")` would start with:
+
+```elixir
+"
+99 bottles of pop on the wall.
+99 bottles of pop.
+Take one down, pass it around.
+98 bottles of pop on the wall.
+"
+```
+
+### Step 7
+
+* Create an `on_the_wall/3` function which accepts an **integer** or a **range** for the first parameter.
+* For the second parameter, the function should accept a **string** for the type of beverage.
+* For the third parameter, the function should accept a **string** for the beverage container.
+* Ensure that `on_the_wall/3` function remains gramatically correct for `0` and `1` beverage container.
+
+For example `BottlesOfSoda.on_the_wall(99, "pop", "can")` would start with:
+
+```elixir
+"
+99 cans of pop on the wall.
+99 cans of pop.
+Take one down, pass it around.
+98 cans of pop on the wall.
+"
+```

exercises/chess_moves.livemd

@@ -0,0 +1,31 @@
+# Chess Moves
+
+## Overview
+
+You're going to a simplified chess game with a 9 X 9 board.
+
+<!-- livebook:{"force_markdown":true} -->
+
+```elixir
+[
+  [nil, nil, nil],
+  [nil, nil, nil],
+  [nil, nil, nil]
+]
+```
+
+You need to create a `Piece` protocol and `can_move?` function
+
+### Create a Checkers Board
+
+* Create a `Checkers` module with a `new` function that returns a fresh checkers board like so,.
+
+<!-- livebook:{"force_markdown":true} -->
+
+```elixir
+[
+  [nil, nil, nil],
+  [nil, nil, nil],
+  [nil, nil, nil]
+]
+```

exercises/custom_rock_paper_scissors.livemd

@@ -0,0 +1,27 @@
+# Rock Paper Scissors
+
+## Custom Rock Paper Scissors
+
+You're going to create a rock paper scissors game where users can create their own choices.
+
+* Create a `CustomGame` struct.
+* Create required keys for `:rock`, `:paper`, `:scissors`.
+* Create a `CustomGame.new/3` function that allows users to enter alternate atoms for `:rock`, `:paper`, and `:scissors`.
+* Create a `CustomGame.play/3` which expects the return value of `CustomGame.create_game/3` as a parameter.
+  The second and third parameter should expect custom atoms the user previously defined.
+
+For example,
+
+```elixir
+game = CustomGame.new(:grass, :fire, :water)
+
+CustomGame.play(game, :fire, :water)
+"water beats fire"
+
+CustomGame.play(game, :water, :water)
+"draw"
+```
+
+```elixir
+
+```