I just added item stacking. It was quite aggravating as I had to redo a lot of the inventory system. But it was definitely worth it. Each item has a specific stack limit. Items can be dragged from any inventory space into any other.
At the moment item dropping is broken due to the fact that it doesn't remove a stack and the house construction system doesn't properly deduct the stack either.
I will try my best to fix the present issues by the end of today and push out the 0.1.0.2 update.