Added seeing intently, and moved disease to creatures.

Seeing intently: normally something at the edge of your vision (unit or animal) might appear as just: there's something there, without knowing what. Seeing intently will reveal what it is for sure, assuming it's still there and hasn't, you
know, eaten you or anything. An action like anything else.
You seeIntently up, down, left, or right. (1,2,3,4). Half your field of view at
once.
You can seeIntently in the direction that your moving. Otherwise, can't do it at the same time as anything else.

Also, diseases are now creature-based instead of unit based, and animals can get
/transmit them.

Added grass. Assuming there's nothing on top, a tile can have grass. If there's no grass, it's dirt. If there's no dirt, it's stone.
Bugfix in creature constructor, forgot to initialize something, bugfix in unit class, forgot to delete a variable that was moved to creature.
Bugfix in food, made rotrate default to 1, so that it doesn't crash when you mod by it.
Bugfix in unit::move, accidentally deleted checking for multitasking at some point.