Add koans for floats, rename to numbers koans, reposition on the list

lib/koans/04_atoms.ex

@@ -1,31 +0,0 @@
-defmodule Atoms do
-  use Koans
-
-  @intro "Atoms"
-
-  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 "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) == ___
-  end
-
-  koan "Functions can be called on the atom too" do
-    assert :"Elixir.String" == String
-    assert :"Elixir.String".upcase("hello") == ___
-  end
-end