Dropping !image[] & other regex fixes

closes #452

- changed keyboard shortcut to insert ![].. not !image[]
- changed regex in ghostdown to only work for ![]
- added a further regex in ghostdown to properly match for URLs inside the parens

ghost/admin/assets/vendor/showdown/extensions/ghostdown.js

@@ -1,14 +1,15 @@
 (function () {
-    var ghostdown = function (converter) {
+    var ghostdown = function () {
         return [
-            // [image] syntax
+            // ![] image syntax
             {
                 type: 'lang',
-                filter: function (source) {
-                    return source.replace(/\n?!(?:image)?\[([^\n\]]*)\](?:\(([^\n\)]*)\))?/gi, function (match, alt, src) {
+                filter: function (text) {
+                    return text.replace(/\n?!\[([^\n\]]*)\](?:\(([^\n\)]*)\))?/gi, function (match, alt, src) {
                         var result = "";
 
-                        if (src !== "http://") {
+                        /* regex from isURL in node-validator. Yum! */
+                        if (src && src.match(/^(?!mailto:)(?:(?:https?|ftp):\/\/)?(?:\S+(?::\S*)?@)?(?:(?:(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[0-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\u00a1-\uffff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)(?:\.(?:[a-z\u00a1-\uffff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)*(?:\.(?:[a-z\u00a1-\uffff]{2,})))|localhost)(?::\d{2,5})?(?:\/[^\s]*)?$/i)) {
                             result = '<img class="js-upload-target" src="' + src + '"/>';
                         }
                         return '<section  class="js-drop-zone image-uploader">' + result +

ghost/admin/markdown-actions.js

@@ -140,7 +140,7 @@
             strike: "~~$1~~",
             code: "`$1`",
             link: "[$1](http://)",
-            image: "!image[$1](http://)",
+            image: "![$1](http://)",
             blockquote: "> $1"
         }
     };

ghost/admin/tpl/modals/markdown.hbs

@@ -34,7 +34,7 @@
         </tr>
         <tr>
             <td>Image</td>
-            <td>!image[image](http://)</td>
+            <td>![alt](http://)</td>
             <td>Ctrl + Shift + I</td>
         </tr>
         <tr>