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/QuerySubmodules.cs

@@ -0,0 +1,44 @@
+using System.Collections.Generic;
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Commands
+{
+    public partial class QuerySubmodules : Command
+    {
+        [GeneratedRegex(@"^[\-\+ ][0-9a-f]+\s(.*)\s\(.*\)$")]
+        private static partial Regex REG_FORMAT1();
+        [GeneratedRegex(@"^[\-\+ ][0-9a-f]+\s(.*)$")]
+        private static partial Regex REG_FORMAT2();
+
+        public QuerySubmodules(string repo)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = "submodule status";
+        }
+
+        public List<string> Result()
+        {
+            Exec();
+            return _submodules;
+        }
+
+        protected override void OnReadline(string line)
+        {
+            var match = REG_FORMAT1().Match(line);
+            if (match.Success)
+            {
+                _submodules.Add(match.Groups[1].Value);
+                return;
+            }
+
+            match = REG_FORMAT2().Match(line);
+            if (match.Success)
+            {
+                _submodules.Add(match.Groups[1].Value);
+            }
+        }
+
+        private readonly List<string> _submodules = new List<string>();
+    }
+}