Move sigils to later in the lessons

While doing this, I also discovered that
there is also a reference to lists in numbers, but
that might a bit easier for someone to grasp, given
the hint that the koan gives, and the output they
see when they run it.

lib/koans/06_lists.ex

@@ -0,0 +1,73 @@
+defmodule Lists do
+  use Koans
+
+  @intro "Lists"
+
+  koan "We can see what is ahead" do
+    assert List.first([1, 2, 3]) == ___
+  end
+
+  koan "Checking what's trailing is also simple" do
+    assert List.last([1, 2, 3]) == ___
+  end
+
+  koan "Lists can store anything you throw at them" do
+    assert [1, 2] ++ [:a, "b"] == ___
+  end
+
+  koan "Things can evolve" do
+    assert [1, 2, 3] -- [3] == ___
+  end
+
+  koan "Evolution can have different forms" do
+    assert List.delete([:a, :b, :c], :b) == ___
+  end
+
+  koan "Precision is also valued" do
+    assert List.delete_at([:a, :b, :c], 2) == ___
+  end
+
+  koan "Replication is also possible" do
+    assert List.duplicate("life", 3) == ___
+  end
+
+  koan "Sometimes leveling the playing field is desired" do
+    assert List.flatten([1, [2, 3], 4, [5]]) == ___
+  end
+
+  koan "Order can also be specified for new members" do
+    assert List.insert_at([1, 2, 3], 1, 4) == ___
+  end
+
+  koan "We can replace things at specified positions" do
+    assert List.replace_at([1, 2, 3], 0, 10) == ___
+  end
+
+  koan "When a replacement cannot be found, the list remains the same" do
+    assert List.replace_at([1, 2, 3], 10, 0) == ___
+  end
+
+  koan "Order is bound by nature's laws" do
+    assert List.insert_at([1, 2, 3], 10, 4) == ___
+  end
+
+  koan "Sometimes it's faster to loop around back" do
+    assert List.insert_at([1, 2, 3], -1, 4) == ___
+  end
+
+  koan "We can also transform ourselves completely" do
+    assert List.to_tuple([1, 2, 3]) == ___
+  end
+
+  koan "Wrapping other values is a handy option" do
+    assert List.wrap("value") == ___
+  end
+
+  koan "Wrapping nothing produces a list of nothing" do
+    assert List.wrap(nil) == ___
+  end
+
+  koan "When there is already a list do not wrap it again" do
+    assert List.wrap(["value"]) == ___
+  end
+end