move version getter into separate class

lib/src/libgit2.dart

@@ -0,0 +1,34 @@
+import 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+import 'package:libgit2dart/libgit2dart.dart';
+import 'package:libgit2dart/src/util.dart';
+
+class Libgit2 {
+  /// Returns libgit2 version number.
+  static String get version {
+    libgit2.git_libgit2_init();
+
+    final major = calloc<Int32>();
+    final minor = calloc<Int32>();
+    final rev = calloc<Int32>();
+    libgit2.git_libgit2_version(major, minor, rev);
+
+    final version = '${major.value}.${minor.value}.${rev.value}';
+
+    calloc.free(major);
+    calloc.free(minor);
+    calloc.free(rev);
+
+    return version;
+  }
+
+  /// Returns list of options libgit2 was compiled with.
+  static Set<GitFeature> get features {
+    libgit2.git_libgit2_init();
+    final featuresInt = libgit2.git_libgit2_features();
+    return GitFeature.values
+        .where((e) => featuresInt & e.value == e.value)
+        .toSet();
+  }
+}