Add MultiPart/MimePart Request Matcher (#981)

* wip

* .

* mm

* x

* .

* .

* .

* tests

* .

* more tests

* trans

* x

* win

* fix

* .

* tests

tools/MultipartUploader/Program.cs

@@ -0,0 +1,17 @@
+namespace MultipartUploader
+{
+    internal static class Program
+    {
+        /// <summary>
+        ///  The main entry point for the application.
+        /// </summary>
+        [STAThread]
+        static void Main()
+        {
+            // To customize application configuration such as set high DPI settings or default font,
+            // see https://aka.ms/applicationconfiguration.
+            ApplicationConfiguration.Initialize();
+            Application.Run(new Form1());
+        }
+    }
+}