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/Discard.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+
+namespace SourceGit.Commands
+{
+    public static class Discard
+    {
+        public static void All(string repo)
+        {
+            new Reset(repo, "HEAD", "--hard").Exec();
+            new Clean(repo).Exec();
+        }
+
+        public static void ChangesInWorkTree(string repo, List<Models.Change> changes)
+        {
+            var needClean = new List<string>();
+            var needCheckout = new List<string>();
+
+            foreach (var c in changes)
+            {
+                if (c.WorkTree == Models.ChangeState.Untracked || c.WorkTree == Models.ChangeState.Added)
+                {
+                    needClean.Add(c.Path);
+                }
+                else
+                {
+                    needCheckout.Add(c.Path);
+                }
+            }
+
+            for (int i = 0; i < needClean.Count; i += 10)
+            {
+                var count = Math.Min(10, needClean.Count - i);
+                new Clean(repo, needClean.GetRange(i, count)).Exec();
+            }
+
+            for (int i = 0; i < needCheckout.Count; i += 10)
+            {
+                var count = Math.Min(10, needCheckout.Count - i);
+                new Checkout(repo).Files(needCheckout.GetRange(i, count));
+            }
+        }
+
+        public static void ChangesInStaged(string repo, List<Models.Change> changes)
+        {
+            for (int i = 0; i < changes.Count; i += 10)
+            {
+                var count = Math.Min(10, changes.Count - i);
+                var files = new List<string>();
+                for (int j = 0; j < count; j++)
+                    files.Add(changes[i + j].Path);
+                new Restore(repo, files, "--staged --worktree").Exec();
+            }
+        }
+    }
+}