feature: add an indicator that shows those commits the current branch ahead/behind its upstream

src/Commands/QueryTrackStatus.cs

@@ -0,0 +1,34 @@
+using System;
+
+namespace SourceGit.Commands
+{
+    public class QueryTrackStatus : Command
+    {
+        public QueryTrackStatus(string repo, string local, string upstream) 
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"rev-list --left-right {local}...{upstream}";
+        }
+
+        public Models.BranchTrackStatus Result()
+        {
+            var status = new Models.BranchTrackStatus();
+
+            var rs = ReadToEnd();
+            if (!rs.IsSuccess)
+                return status;
+
+            var lines = rs.StdOut.Split(['\n', '\r'], StringSplitOptions.RemoveEmptyEntries);
+            foreach (var line in lines)
+            {
+                if (line[0] == '>')
+                    status.Behind.Add(line.Substring(1));
+                else
+                    status.Ahead.Add(line.Substring(1));
+            }
+
+            return status;
+        }
+    }
+}