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/Models/User.cs

@@ -0,0 +1,46 @@
+using System.Collections.Generic;
+
+namespace SourceGit.Models
+{
+    public class User
+    {
+        public static readonly User Invalid = new User();
+
+        public string Name { get; set; } = string.Empty;
+        public string Email { get; set; } = string.Empty;
+
+        public override bool Equals(object obj)
+        {
+            if (obj == null || !(obj is User))
+                return false;
+
+            var other = obj as User;
+            return Name == other.Name && Email == other.Email;
+        }
+
+        public override int GetHashCode()
+        {
+            return base.GetHashCode();
+        }
+
+        public static User FindOrAdd(string data)
+        {
+            if (_caches.TryGetValue(data, out var value))
+            {
+                return value;
+            }
+            else
+            {
+                var nameEndIdx = data.IndexOf('<', System.StringComparison.Ordinal);
+                var name = nameEndIdx >= 2 ? data.Substring(0, nameEndIdx - 1) : string.Empty;
+                var email = data.Substring(nameEndIdx + 1);
+
+                User user = new User() { Name = name, Email = email };
+                _caches.Add(data, user);
+                return user;
+            }
+        }
+
+        private static Dictionary<string, User> _caches = new Dictionary<string, User>();
+    }
+}