project: reorganize the structure of the project.

* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.

src/Commands/SaveRevisionFile.cs

@@ -0,0 +1,81 @@
+using System;
+using System.Diagnostics;
+using System.IO;
+
+using Avalonia.Threading;
+
+namespace SourceGit.Commands
+{
+    public static class SaveRevisionFile
+    {
+        public static void Run(string repo, string revision, string file, string saveTo)
+        {
+            var isLFSFiltered = new IsLFSFiltered(repo, file).Result();
+            if (isLFSFiltered)
+            {
+                var tmpFile = saveTo + ".tmp";
+                if (ExecCmd(repo, $"show {revision}:\"{file}\"", tmpFile))
+                {
+                    ExecCmd(repo, $"lfs smudge", saveTo, tmpFile);
+                }
+                File.Delete(tmpFile);
+            }
+            else
+            {
+                ExecCmd(repo, $"show {revision}:\"{file}\"", saveTo);
+            }
+        }
+
+        private static bool ExecCmd(string repo, string args, string outputFile, string inputFile = null)
+        {
+            var starter = new ProcessStartInfo();
+            starter.WorkingDirectory = repo;
+            starter.FileName = Native.OS.GitInstallPath;
+            starter.Arguments = args;
+            starter.UseShellExecute = false;
+            starter.CreateNoWindow = true;
+            starter.WindowStyle = ProcessWindowStyle.Hidden;
+            starter.RedirectStandardInput = true;
+            starter.RedirectStandardOutput = true;
+            starter.RedirectStandardError = true;
+
+            using (var sw = File.OpenWrite(outputFile))
+            {
+                try
+                {
+                    var proc = new Process() { StartInfo = starter };
+                    proc.Start();
+
+                    if (inputFile != null)
+                    {
+                        using (StreamReader sr = new StreamReader(inputFile))
+                        {
+                            while (true)
+                            {
+                                var line = sr.ReadLine();
+                                if (line == null)
+                                    break;
+                                proc.StandardInput.WriteLine(line);
+                            }
+                        }
+                    }
+
+                    proc.StandardOutput.BaseStream.CopyTo(sw);
+                    proc.WaitForExit();
+                    var rs = proc.ExitCode == 0;
+                    proc.Close();
+
+                    return rs;
+                }
+                catch (Exception e)
+                {
+                    Dispatcher.UIThread.Invoke(() =>
+                    {
+                        App.RaiseException(repo, "Save file failed: " + e.Message);
+                    });
+                    return false;
+                }
+            }
+        }
+    }
+}