Added markdown extra as a dependency

Author: happyaccidents

composer.json

@@ -4,7 +4,8 @@
     "keywords": ["markdown", "html", "converter"],
     "license": "MIT",
     "require": {
-        "php": ">=5.4"
+        "php": ">=5.4",
+        "dflydev/markdown": "1.*"
     },
     "authors": [
         {