Necrofy properties

Necrofy v2 and later stores some metadata in the ROM files it builds. The data is located at $82:D1EE. This location was originally used for storing secret item bonus types, but Necrofy moves that into the level data. The format is as follows:

Offset	Length	Type	Description
0x00	3	string	Always contains the string "NFY" in ASCII
0x03	1	byte	Version. Current version is 2
0x04	4	pointer32	Pointer to extra sprite graphics
0x08	4	pointer32	Pointer to the end of the extra sprite graphics