Add functionality to the AECode parser to process strings inside strings

The syntax to be searched for inside the string will be:
<aecode>{&INSTRUCTIONS&}</aecode>
NOTE: The tags are case sensitive.
NOTE: The instructions are parsed like regular AECode.

In order to prevent the string to be parsed, the < and > charactershave to be escaped with their corresponding HTML entities. The main aim of this function is to be used in the HTML mode of the TextWidget, allowing the user to insert dynamic content.

The function called by the TextWidget in HTML mode is AECparse_tags_replace(&$string, &$dataarray = array()).
Both variables are supplied by reference. The $string is the string containing the tags to be processed and replaced.