Add XmlPath2 / RegEx matchers

Solves issue #5

src/WireMock/Matchers/XPathMatcher.cs

@@ -0,0 +1,42 @@
+using System.Xml;
+using JetBrains.Annotations;
+using WireMock.Validation;
+using Wmhelp.XPath2;
+
+namespace WireMock.Matchers
+{
+    /// <summary>
+    /// XPath2Matcher
+    /// </summary>
+    /// <seealso cref="WireMock.Matchers.IMatcher" />
+    public class XPathMatcher : IMatcher
+    {
+        private readonly string _pattern;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="XPathMatcher"/> class.
+        /// </summary>
+        /// <param name="pattern">The pattern.</param>
+        public XPathMatcher([NotNull] string pattern)
+        {
+            Check.NotNull(pattern, nameof(pattern));
+
+            _pattern = pattern;
+        }
+
+        /// <summary>
+        /// Determines whether the specified input is match.
+        /// </summary>
+        /// <param name="input">The input.</param>
+        /// <returns>
+        ///   <c>true</c> if the specified input is match; otherwise, <c>false</c>.
+        /// </returns>
+        public bool IsMatch(string input)
+        {
+            var nav = new XmlDocument { InnerXml = input }.CreateNavigator();
+            object result = nav.XPath2Evaluate($"boolean({_pattern})");
+
+            return true.Equals(result);
+        }
+    }
+}