reference: add id() to get the sha

src/geef.erl

@@ -2,7 +2,7 @@
 -export([hex_to_raw/1, repository/1, repository_get_path/1, repository_get_odb/1,
 	 repository_init/2, repository_is_bare/1, repository_get_workdir/1, reference_list/1,
 	 reference_to_id/2, reference_glob/2, reference_lookup/2, reference_resolve/1,
-	 odb_object_exists/2]).
+	 reference_id/1, odb_object_exists/2]).
 -on_load(load_enif/0).
 
 hex_to_raw(_Val) ->
@@ -38,6 +38,9 @@ reference_glob(_Repo, _Glob) ->
 reference_lookup(_Repo, _Refname) ->
     nif_error(?LINE).
 
+reference_id(_Handle) ->
+    nif_error(?LINE).
+
 reference_resolve(_Handle) ->
     nif_error(?LINE).
 

src/reference.erl

@@ -1,5 +1,5 @@
 -module(reference, [Handle]).
--export([resolve/0]).
+-export([resolve/0, id/0]).
 
 resolve() ->
     case geef:reference_resolve(Handle) of
@@ -8,3 +8,7 @@ resolve() ->
 	Other ->
 	    Other
     end.
+
+-spec id() -> binary().
+id() ->
+    geef:reference_id(Handle).