Stef negate matcher (#134)

* RejectOnMatch (wip)

* RejectOnMatch (wip)

* RejectOnMatch (wip)

* RejectOnMatch (wip)

* docs: improve sample app matcher to show use of reject on match

* Reworked code review comments

src/WireMock.Net/Matchers/MatchBehaviour.cs

@@ -0,0 +1,18 @@
+namespace WireMock.Matchers
+{
+    /// <summary>
+    /// MatchBehaviour
+    /// </summary>
+    public enum MatchBehaviour
+    {
+        /// <summary>
+        /// Accept on match (default)
+        /// </summary>
+        AcceptOnMatch,
+
+        /// <summary>
+        /// Reject on match
+        /// </summary>
+        RejectOnMatch
+    }
+}