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/Clone.cs

@@ -0,0 +1,40 @@
+using System;
+
+namespace SourceGit.Commands
+{
+    public class Clone : Command
+    {
+        private readonly Action<string> _notifyProgress;
+
+        public Clone(string ctx, string path, string url, string localName, string sshKey, string extraArgs, Action<string> ouputHandler)
+        {
+            Context = ctx;
+            WorkingDirectory = path;
+            TraitErrorAsOutput = true;
+
+            if (string.IsNullOrEmpty(sshKey))
+            {
+                Args = "-c credential.helper=manager ";
+            }
+            else
+            {
+                Args = $"-c core.sshCommand=\"ssh -i '{sshKey}'\" ";
+            }
+
+            Args += "clone --progress --verbose --recurse-submodules ";
+
+            if (!string.IsNullOrEmpty(extraArgs))
+                Args += $"{extraArgs} ";
+            Args += $"{url} ";
+            if (!string.IsNullOrEmpty(localName))
+                Args += localName;
+
+            _notifyProgress = ouputHandler;
+        }
+
+        protected override void OnReadline(string line)
+        {
+            _notifyProgress?.Invoke(line);
+        }
+    }
+}