feature<SubTree>: supports git subtree feature

src/Commands/SubTree.cs

@@ -0,0 +1,39 @@
+using System;
+
+namespace SourceGit.Commands {
+    /// <summary>
+    ///     子树相关操作
+    /// </summary>
+    public class SubTree : Command {
+        private Action<string> handler = null;
+
+        public SubTree(string repo) {
+            Cwd = repo;
+            TraitErrorAsOutput = true;
+        }
+
+        public override void OnReadline(string line) {
+            handler?.Invoke(line);
+        }
+
+        public bool Add(string prefix, string source, string revision, bool squash, Action<string> onProgress) {
+            handler = onProgress;
+            Args = $"subtree add --prefix=\"{prefix}\" {source} {revision}";
+            if (squash) Args += " --squash";
+            return Exec();
+        }
+
+        public void Pull(string prefix, string source, string branch, bool squash, Action<string> onProgress) {
+            handler = onProgress;
+            Args = $"subtree pull --prefix=\"{prefix}\" {source} {branch}";
+            if (squash) Args += " --squash";
+            Exec();
+        }
+
+        public void Push(string prefix, string source, string branch, Action<string> onProgress) {
+            handler = onProgress;
+            Args = $"subtree push --prefix=\"{prefix}\" {source} {branch}";
+            Exec();
+        }
+    }
+}