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/AssumeUnchanged.cs

@@ -0,0 +1,75 @@
+using System.Collections.Generic;
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Commands
+{
+    public partial class AssumeUnchanged
+    {
+        partial class ViewCommand : Command
+        {
+            [GeneratedRegex(@"^(\w)\s+(.+)$")]
+            private static partial Regex REG();
+
+            public ViewCommand(string repo)
+            {
+                WorkingDirectory = repo;
+                Args = "ls-files -v";
+                RaiseError = false;
+            }
+
+            public List<string> Result()
+            {
+                Exec();
+                return _outs;
+            }
+
+            protected override void OnReadline(string line)
+            {
+                var match = REG().Match(line);
+                if (!match.Success)
+                    return;
+
+                if (match.Groups[1].Value == "h")
+                {
+                    _outs.Add(match.Groups[2].Value);
+                }
+            }
+
+            private readonly List<string> _outs = new List<string>();
+        }
+
+        class ModCommand : Command
+        {
+            public ModCommand(string repo, string file, bool bAdd)
+            {
+                var mode = bAdd ? "--assume-unchanged" : "--no-assume-unchanged";
+
+                WorkingDirectory = repo;
+                Context = repo;
+                Args = $"update-index {mode} -- \"{file}\"";
+            }
+        }
+
+        public AssumeUnchanged(string repo)
+        {
+            _repo = repo;
+        }
+
+        public List<string> View()
+        {
+            return new ViewCommand(_repo).Result();
+        }
+
+        public void Add(string file)
+        {
+            new ModCommand(_repo, file, true).Exec();
+        }
+
+        public void Remove(string file)
+        {
+            new ModCommand(_repo, file, false).Exec();
+        }
+
+        private readonly string _repo;
+    }
+}