Add the isogram exercise (exercism#220)

* Add isogram exercise.

* Change tests by principle: one test - one feature

* Changed the order of words in the test names

Author: jimmbraddock

config.json

@@ -25,6 +25,7 @@
     "hamming",
     "triangle",
     "beer-song",
+    "isogram",
     "grade-school",
     "list-ops",
     "flatten-array",

exercises/isogram/example.exs

@@ -0,0 +1,15 @@
+defmodule Isogram do
+  @doc """
+  Determines if a word or sentence is an isogram
+  """
+  @spec isogram?(String.t) :: boolean
+  def isogram?(sentence) do
+    codepoints = sentence
+      |> String.downcase
+      |> String.replace(~r/\s|-/u, "")
+      |> String.codepoints
+
+    length(Enum.uniq(codepoints)) == length(codepoints)
+  end
+
+end

exercises/isogram/isogram.exs

@@ -0,0 +1,10 @@
+defmodule Isogram do
+  @doc """
+  Determines if a word or sentence is an isogram
+  """
+  @spec isogram?(String.t) :: boolean
+  def isogram?(sentence) do
+
+  end
+
+end

exercises/isogram/isogram_test.exs

@@ -0,0 +1,60 @@
+if !System.get_env("EXERCISM_TEST_EXAMPLES") do
+  Code.load_file("isogram.exs", __DIR__)
+end
+
+ExUnit.start
+ExUnit.configure exclude: :pending, trace: true
+
+defmodule IsogramTest do
+  use ExUnit.Case
+
+  test "isogram lowercase" do
+    assert Isogram.isogram?("subdermatoglyphic")
+  end
+
+  @tag :pending
+  test "not isogram lowercase " do
+    refute Isogram.isogram?("eleven")
+  end
+
+  @tag :pending
+  test "isogram uppercase" do
+    assert Isogram.isogram?("DEMONSTRABLY")
+  end
+
+  @tag :pending
+  test "not isogram uppercase" do
+    refute Isogram.isogram?("ALPHABET")
+  end
+
+  @tag :pending
+  test "isogram with dash" do
+    assert Isogram.isogram?("hjelmqvist-gryb-zock-pfund-wax")
+  end
+
+  @tag :pending
+  test "not isogram with dash" do
+    refute Isogram.isogram?("twenty-five")
+  end
+
+  @tag :pending
+  test "isogram with utf-8 letters" do
+    assert Isogram.isogram?("heizölrückstoßabdämpfung")
+  end
+
+  @tag :pending
+  test "not isogram with utf-8 letters" do
+    refute Isogram.isogram?("éléphant")
+  end
+
+  @tag :pending
+  test "phrase is isogram" do
+    assert Isogram.isogram?("emily jung schwartzkopf")
+  end
+
+  @tag :pending
+  test "phrase is not isogram" do
+    refute Isogram.isogram?("the quick brown fox")
+  end
+
+end