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/Rebase.cs

@@ -0,0 +1,15 @@
+namespace SourceGit.Commands
+{
+    public class Rebase : Command
+    {
+        public Rebase(string repo, string basedOn, bool autoStash)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = "rebase ";
+            if (autoStash)
+                Args += "--autostash ";
+            Args += basedOn;
+        }
+    }
+}