support wrap function in bbcode rules

app/assets/javascripts/pretty-text/engines/markdown-it/bbcode-block.js.es6

@@ -213,16 +213,33 @@ function applyBBCode(state, startLine, endLine, silent, md) {
 
     let wrapTag;
     if (rule.wrap) {
+      let token;
+
+      if (typeof rule.wrap === 'function') {
+        token = new state.Token('wrap_bbcode', 'div', 1);
+        token.level = state.level+1;
+
+        if (!rule.wrap(token, info)) {
+          return false;
+        }
+
+        state.tokens.push(token);
+        state.level = token.level;
+        wrapTag = token.tag;
+
+      } else {
+
         let split = rule.wrap.split('.');
         wrapTag = split[0];
         let className = split.slice(1).join(' ');
 
-      let token = state.push('wrap_bbcode', wrapTag, 1);
+        token = state.push('wrap_bbcode', wrapTag, 1);
 
         if (className) {
           token.attrs = [['class', className]];
         }
       }
+    }
 
     let lastToken = state.tokens[state.tokens.length-1];
     lastToken.map    = [ startLine, nextLine ];