move version getter into separate class

test/libgit2_test.dart

@@ -0,0 +1,19 @@
+import 'package:libgit2dart/libgit2dart.dart';
+import 'package:libgit2dart/src/libgit2.dart';
+import 'package:libgit2dart/src/util.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Libgit2', () {
+    test('returns up to date version of libgit2', () {
+      expect(Libgit2.version, libgit2Version);
+    });
+
+    test('returns list of options libgit2 was compiled with', () {
+      expect(
+        Libgit2.features,
+        {GitFeature.threads, GitFeature.https, GitFeature.ssh, GitFeature.nsec},
+      );
+    });
+  });
+}