well txt is possible but html files i think not
yes, any files is possible
(
this game is 100% html and JS)
two steps u need to do:
1. create new template with name of your files exetension (i.e. txt.html ) and place it in /templates/<yourtemplate>/media/ folder (look in jpg.html template for the avalable tags).
2. add the extension in 4images settings