Handheld game system

Added a handheld game system (deliberately named to not indicate any particular real-world counterpart).

It essentially acts like a superbook; it gives a big morale bonus and (thanks to a backlight) can be used in the dark, but it requires batteries and leaves you oblivious to your surroundings while being used.

It can be found anywhere that an MP3 player can be found, but is a little rarer. Has a slightly higher chance of being found in an electronics store. It can be disassembled and has a high-level crafting recipe, including a new "small LCD screen" item that could potentially be used by other recipes in the future.

Comments welcome, especially regarding balance and the item recipes/values.