Added coding style modes to SimpleMDE (#3286)

* Added coding style modes to SimpleMDE

* Moved the CodeMirror addon from simplemd to codemirror directory

public/plugins/codemirror-5.17.0/mode/diff/diff.js

@@ -0,0 +1,47 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: http://codemirror.net/LICENSE
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+"use strict";
+
+CodeMirror.defineMode("diff", function() {
+
+  var TOKEN_NAMES = {
+    '+': 'positive',
+    '-': 'negative',
+    '@': 'meta'
+  };
+
+  return {
+    token: function(stream) {
+      var tw_pos = stream.string.search(/[\t ]+?$/);
+
+      if (!stream.sol() || tw_pos === 0) {
+        stream.skipToEnd();
+        return ("error " + (
+          TOKEN_NAMES[stream.string.charAt(0)] || '')).replace(/ $/, '');
+      }
+
+      var token_name = TOKEN_NAMES[stream.peek()] || stream.skipToEnd();
+
+      if (tw_pos === -1) {
+        stream.skipToEnd();
+      } else {
+        stream.pos = tw_pos;
+      }
+
+      return token_name;
+    }
+  };
+});
+
+CodeMirror.defineMIME("text/x-diff", "diff");
+
+});