Fix issue #373 problems in urls with special characters

Added function to escape URLs entered via JS prompt.

It's a partial fix because people cannot be stopped entering URLs manually and forgetting to escape them.

src/js/easymde.js

@@ -848,6 +848,8 @@ function drawLink(editor) {
         if (!url) {
             return false;
         }
+
+        if (/[()<>]/.test(url)) url = escapeUrl(url);
     }
     _replaceSelection(cm, stat.link, options.insertTexts.link, url);
 }
@@ -865,10 +867,26 @@ function drawImage(editor) {
         if (!url) {
             return false;
         }
+
+        if (/[()<>]/.test(url)) url = escapeUrl(url);
     }
     _replaceSelection(cm, stat.image, options.insertTexts.image, url);
 }
 
+/**
+ * Escape URLs to prevent breaking up rendered Markdown links
+ * @param url {string} The url of the link or image
+ */
+function escapeUrl(url) {
+
+    url = url.replace(/\(/g,'\\(')
+             .replace(/\)/g,'\\)')
+             .replace(/</g,'\\<')
+             .replace(/>/g,'\\>');
+
+    return url;
+}
+
 /**
  * Action for opening the browse-file window to upload an image to a server.
  * @param editor {EasyMDE} The EasyMDE object