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/IsBinary.cs

@@ -0,0 +1,23 @@
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Commands
+{
+    public partial class IsBinary : Command
+    {
+        [GeneratedRegex(@"^\-\s+\-\s+.*$")]
+        private static partial Regex REG_TEST();
+
+        public IsBinary(string repo, string commit, string path)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"diff 4b825dc642cb6eb9a060e54bf8d69288fbee4904 {commit} --numstat -- \"{path}\"";
+            RaiseError = false;
+        }
+
+        public bool Result()
+        {
+            return REG_TEST().IsMatch(ReadToEnd().StdOut);
+        }
+    }
+}