Wrap commit creation in elixir

lib/geef/commit.ex

@@ -1,7 +1,11 @@
 defmodule Geef.Commit do
   alias Geef.Object
+  alias Geef.Signature
+  alias Geef.Oid
   import Object, only: :macros
 
+  @type t :: Object[type: :commit]
+
   def lookup(repo, id) do
     case :geef_commit.lookup(repo, id) do
       {:ok, commit} ->
@@ -15,4 +19,9 @@ defmodule Geef.Commit do
     :geef_commit.tree_id(rebind(commit))
   end
 
+  @type create(pid, Signature.t, Signature.t, iolist, Tree.t, Commit.t, [atom]) :: {:ok, Oid.t} | {:error, term}
+  def create(repo, author = Signature[], committer = Signature[], message, tree, parents, opts // []) do
+    :geef_commit.create(repo, author, committer, message, tree, parents, opts)
+  end
+
 end

lib/geef/tree.ex

@@ -11,6 +11,8 @@ defrecord Geef.Tree, Record.extract(:geef_object, from: "src/geef_records.hrl")
 
   import Object, only: :macros
 
+  @type t :: Object[type: :commit]
+
   def lookup(repo, id) do
     case :geef_tree.lookup(repo, id) do
       {:ok, obj} ->