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/Restore.cs

@@ -0,0 +1,23 @@
+using System.Collections.Generic;
+using System.Text;
+
+namespace SourceGit.Commands
+{
+    public class Restore : Command
+    {
+        public Restore(string repo, List<string> files, string extra)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+
+            StringBuilder builder = new StringBuilder();
+            builder.Append("restore ");
+            if (!string.IsNullOrEmpty(extra))
+                builder.Append(extra).Append(" ");
+            builder.Append("--");
+            foreach (var f in files)
+                builder.Append(' ').Append('"').Append(f).Append('"');
+            Args = builder.ToString();
+        }
+    }
+}