The source code is pretty amazing honestly. It's so ridiculously simplistic that I can alter it for pretty much any crafting system I want.
It took me less than 10 minutes to add "Magic Gem" which is Magic + Diamond... And If I wasn't going on nearly 20 hours of no sleep I'm sure I could easily make the crafting slots into a 4x4 or even 16x16 grid if I really wanted to 
Great game 10/10!