feat(reference): add ability to get shorthand name of reference

lib/src/bindings/reference.dart

@@ -73,6 +73,15 @@ String name(Pointer<git_reference> ref) {
   return result.cast<Utf8>().toDartString();
 }
 
+/// Get the reference's short name.
+///
+/// This will transform the reference name into a name "human-readable" version.
+/// If no shortname is appropriate, it will return the full name.
+String shorthand(Pointer<git_reference> ref) {
+  final result = libgit2.git_reference_shorthand(ref);
+  return result.cast<Utf8>().toDartString();
+}
+
 /// Fill a list with all the references that can be found in a repository.
 ///
 /// The string array will be filled with the names of all references;

lib/src/reference.dart

@@ -165,6 +165,12 @@ class Reference {
   /// Returns the full name of a reference.
   String get name => bindings.name(_refPointer);
 
+  /// Returns the reference's short name.
+  ///
+  /// This will transform the reference name into a name "human-readable" version.
+  /// If no shortname is appropriate, it will return the full name.
+  String get shorthand => bindings.shorthand(_refPointer);
+
   /// Returns a list with all the references that can be found in a repository.
   ///
   /// Throws a [LibGit2Error] if error occured.

test/reference_test.dart

@@ -272,11 +272,25 @@ void main() {
       ref.free();
     });
 
-    test('returns the full name of a reference', () {
+    test('returns the full name', () {
       expect(repo.head.name, 'refs/heads/master');
       repo.head.free();
     });
 
+    test('returns the short name', () {
+      final ref = repo.createReference(
+        name: 'refs/remotes/origin/master',
+        target: lastCommit,
+      );
+
+      expect(repo.head.shorthand, 'master');
+      expect(ref.shorthand, 'origin/master');
+
+      repo.head.free();
+      ref.delete();
+      ref.free();
+    });
+
     test('returns a map with all the references of repository', () {
       expect(
         repo.references,