Nanospray

I have never contributed to DDA before, or any other projects here on GitHub. In fact, this is my first time messing with Git, really. It's been a good few years since I even looked at a piece of C++ and I really don't code much of anything that often, but I have wanted to add something to DDA for a while.

As a start back into my C++ fiddling I added this bit of code based on what was already in the game (as I have pretty minimal experience with C++ I probably can't write something from scratch just yet).

I have playtested what I added here a good bit. It seems alright to me, though it may need to be rebalanced a bit.

Anyway, I added a new item: a canister of nanobots that can be found in labs (if I did this right, I hope?). Activating it will prompt the player for a direction (like how the lighter does) and will place a field of nanobots on the map dealing damage to the player and enemies as well. The damage model did seem alright to me, but it may need to be tweaked a bit?

Originally this was going to be an antiviral spray as you can tell from the first few commits, but I changed it over to nanobots because I realized I really don't know much about the lore of the game. I didn't think it would be fitting to add something that might not even make sense to harm the zombies. After all, as far as I know they are not virally infected humans.

I also noticed a typo in the new zlave stuff in game.cpp. Fixed that as well.