feat(tag): add bindings and api

lib/src/bindings/object.dart

@@ -1,6 +1,41 @@
 import 'dart:ffi';
+import 'package:ffi/ffi.dart';
 import 'libgit2_bindings.dart';
+import '../error.dart';
 import '../util.dart';
 
 /// Get the object type of an object.
 int type(Pointer<git_object> obj) => libgit2.git_object_type(obj);
+
+/// Lookup a reference to one of the objects in a repository.
+///
+/// The generated reference is owned by the repository and should be closed with
+/// the `free()` method instead of free'd manually.
+///
+/// The 'type' parameter must match the type of the object in the odb; the method will
+/// fail otherwise. The special value 'GIT_OBJECT_ANY' may be passed to let the method
+/// guess the object's type.
+///
+/// Throws a [LibGit2Error] if error occured.
+Pointer<git_object> lookup(
+  Pointer<git_repository> repo,
+  Pointer<git_oid> id,
+  int type,
+) {
+  final out = calloc<Pointer<git_object>>();
+  final error = libgit2.git_object_lookup(out, repo, id, type);
+
+  if (error < 0) {
+    throw LibGit2Error(libgit2.git_error_last());
+  } else {
+    return out.value;
+  }
+}
+
+/// Close an open object to release memory.
+///
+/// This method instructs the library to close an existing object; note that git_objects
+/// are owned and cached by the repository so the object may or may not be freed after
+/// this library call, depending on how aggressive is the caching mechanism used by
+/// the repository.
+void free(Pointer<git_object> object) => libgit2.git_object_free(object);