The game has a working level editor, but it's undocumented... it may be a little hard to figure out how to use it without documentation, but you're welcome to try... (Hint: You can select the current tile type by pressing different keys, and then place tiles with the mouse.)

The "Read Code" button is related to the level editor... when you create a level you can get a code that can be entered into the text box at the bottom; if you have a valid code entered there, then "Read Code" will load the level (and allow you to play it, if you're on the playing screen rather than the editing screen).

You can see more information about the creation of the game at my blog, Comparative Creation (http://comparativecreation.blogspot.com/search/label/underequipped).