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/SaveChangesAsPatch.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+
+using Avalonia.Threading;
+
+namespace SourceGit.Commands
+{
+    public static class SaveChangesAsPatch
+    {
+        public static bool Exec(string repo, List<Models.Change> changes, bool isUnstaged, string saveTo)
+        {
+            using (var sw = File.Create(saveTo))
+            {
+                foreach (var change in changes)
+                {
+                    if (!ProcessSingleChange(repo, new Models.DiffOption(change, isUnstaged), sw))
+                        return false;
+                }
+            }
+
+            return true;
+        }
+
+        private static bool ProcessSingleChange(string repo, Models.DiffOption opt, FileStream writer)
+        {
+            var starter = new ProcessStartInfo();
+            starter.WorkingDirectory = repo;
+            starter.FileName = Native.OS.GitInstallPath;
+            starter.Arguments = $"diff --ignore-cr-at-eol --unified=4 {opt}";
+            starter.UseShellExecute = false;
+            starter.CreateNoWindow = true;
+            starter.WindowStyle = ProcessWindowStyle.Hidden;
+            starter.RedirectStandardOutput = true;
+
+            try
+            {
+                var proc = new Process() { StartInfo = starter };
+                proc.Start();
+                proc.StandardOutput.BaseStream.CopyTo(writer);
+                proc.WaitForExit();
+                var rs = proc.ExitCode == 0;
+                proc.Close();
+
+                return rs;
+            }
+            catch (Exception e)
+            {
+                Dispatcher.UIThread.Invoke(() =>
+                {
+                    App.RaiseException(repo, "Save change to patch failed: " + e.Message);
+                });
+                return false;
+            }
+        }
+    }
+}