Warn about a potential TFC duplication

[Xymanek]

Since switching to DLC cooking functionality (#46) the cooker no longer keeps track of what's inside the mod's TFCs, causing it to duplicate the data there during incremental cooking. While we can't prevent that, we could warn the mod devs about such possibility:

1. When a .tfc is created, record its initial size
2. When the size grows to twice the original, print a warning promoting the mod devs to do a full rebuild

[Xymanek]

No longer relevant as DLC cook was reverted (#53)

[Xymanek]

DLC cooking was re-implemented in #70, which also implemented the warning functionality