Add atom koans

lib/koans/03_atoms.ex

@@ -0,0 +1,39 @@
+defmodule Atoms do
+  use Koans
+
+  koan "Atoms are sort of like strings" do
+    adam = :human
+    assert adam == ___
+  end
+
+  koan "Strings can be converted to atoms, and vice versa" do
+    assert String.to_atom("atomized") == ___
+    assert Atom.to_string(:stringified) == ___
+  end
+
+  koan "Atoms are often used as keys, because they're faster than strings" do
+    map = %{name: "Jay"}
+    list = [name: "Jay"]
+
+    assert map[:name] == ___
+    assert list[:name] == ___
+  end
+
+  koan "It is surprising to find out that booleans are atoms" do
+    assert is_atom(true) == ___
+    assert is_atom(false) == ___
+    assert :true == ___
+    assert :false == ___
+  end
+
+  koan "Modules are also atoms" do
+    assert is_atom(String) == ___
+    assert :"Elixir.String" == ___
+    assert :"Elixir.String".upcase("hello") == ___
+  end
+
+  koan "Atoms are used to access Erlang" do
+    assert :erlang.is_list([]) == ___
+    assert :lists.sort([2, 3, 1]) == ___
+  end
+end