Add DefinitionBook configurable to replace definition data

src/Parsedown.php

@@ -42,9 +42,6 @@ class Parsedown
 
     protected function textElements($text)
     {
-        # make sure no definitions are set
-        $this->DefinitionData = [];
-
         # iterate through lines to identify blocks
         return $this->linesElements(Lines::fromTextLines($text, 0));
     }
@@ -1739,12 +1736,6 @@ class Parsedown
 
     private static $instances = [];
 
-    #
-    # Fields
-    #
-
-    protected $DefinitionData;
-
     #
     # Read-Only