Support Microsoft.AspNetCore for net 4.6.1 and up (#185)

* net451

* tests : net462

* fixed tests

* fix tests

* readme

* Code review

* LocalFileSystemHandlerTests

* refactor

examples/WireMock.Net.Console.Net452.Classic/CustomFileSystemFileHandler.cs

@@ -0,0 +1,47 @@
+using System.Collections.Generic;
+using System.IO;
+using WireMock.Handlers;
+
+namespace WireMock.Net.ConsoleApplication
+{
+    internal class CustomFileSystemFileHandler : IFileSystemHandler
+    {
+        private static readonly string AdminMappingsFolder = Path.Combine("__admin", "mappings");
+
+        /// <inheritdoc cref="IFileSystemHandler.FolderExists"/>
+        public bool FolderExists(string path)
+        {
+            return Directory.Exists(path);
+        }
+
+        /// <inheritdoc cref="IFileSystemHandler.CreateFolder"/>
+        public void CreateFolder(string path)
+        {
+            Directory.CreateDirectory(path);
+        }
+
+        /// <inheritdoc cref="IFileSystemHandler.EnumerateFiles"/>
+        public IEnumerable<string> EnumerateFiles(string path)
+        {
+            return Directory.EnumerateFiles(path);
+        }
+
+        /// <inheritdoc cref="IFileSystemHandler.GetMappingFolder"/>
+        public string GetMappingFolder()
+        {
+            return Path.Combine(@"c:\temp-wiremock", AdminMappingsFolder);
+        }
+
+        /// <inheritdoc cref="IFileSystemHandler.ReadMappingFile"/>
+        public string ReadMappingFile(string path)
+        {
+            return File.ReadAllText(path);
+        }
+
+        /// <inheritdoc cref="IFileSystemHandler.WriteMappingFile"/>
+        public void WriteMappingFile(string path, string text)
+        {
+            File.WriteAllText(path, text);
+        }
+    }
+}