feat(Changex.Formatter.Elixir): pass options list instead of version

The version argument that is passed through to the elixir parser is now
a keyword list. This will easily enable other options to be passed in
the future (such as the GitHub url)

The other formatter will be changed to a similar format in the future.

BREAKING CHANGE: Calling `Changex.Formatter.Elixir.format` with a string
as the second argument is no longer valid. Instead you can call
`Changex.Formatter.Elixir.format` with an options list as the second
argument. This list can contain a `version` key.

lib/changex/formatter/elixir.ex

@@ -35,8 +35,8 @@ defmodule Changex.Formatter.Elixir do
         * [Scope 2] commit 8
 
   """
-  def format(commits, version \\ nil) do
-    heading(version) <> types(commits)
+  def format(commits, options \\ []) do
+    heading(Keyword.get(options, :version)) <> types(commits)
   end
 
   defp heading(version) do

lib/mix/tasks/changex/diff.ex

@@ -81,7 +81,7 @@ defmodule Mix.Tasks.Changex.Diff do
     Changex.Formatter.Markdown.format(commits, version) |> IO.puts
   end
   defp output(commits, "elixir", version) do
-    Changex.Formatter.Elixir.format(commits, version) |> IO.puts
+    Changex.Formatter.Elixir.format(commits, version: version) |> IO.puts
   end
   defp output(commits, formatter, version) do
     apply(Module.concat([formatter]), :format, [commits, version])

test/changex/formatter/elixir_test.exs

@@ -19,7 +19,7 @@ defmodule Changex.Formatter.ElixirTest do
   end
 
   test "Formatting with an explicit version", %{commits: commits} do
-    assert Changex.Formatter.Elixir.format(commits, "v10") == expected_markdown("v10")
+    assert Changex.Formatter.Elixir.format(commits, version: "v10") == expected_markdown("v10")
   end
 
   test "Formatting with an implicit version", %{commits: commits} do
@@ -37,7 +37,7 @@ defmodule Changex.Formatter.ElixirTest do
     * Bug fixes
       * [policy] remove reference to data retention length
     """ |> String.rstrip
-    assert Changex.Formatter.Elixir.format(commits, "v10") == expected
+    assert Changex.Formatter.Elixir.format(commits, version: "v10") == expected
   end
 
   defp expected_markdown(version) do