Monster rebalance and lots of new animals

This is the first of some updates I've been working on for DDA's flora and fauna.  

Existing creatures are generally rebalanced for difficulty.  Zombies are a little stronger, but not extremely so.  They'll still fall by the thousands against a powerful combatant, but completely untalented fighters will need to be more careful in the beginning than they might have been before.

Later-game enemies were made stronger, substantially so in some cases.  Animals were given more behavior triggers to simulate more realistic wild animal behavior (most non-mutant animals will try to avoid the player if possible, but tougher ones will fight if pursued).  More predatory animals will be interesting in attacking a weak player.  This should help regulate the cliff racer style, suicidal annoyance attacks of certain kinds of wildlife.

I know that there's been some adjustment made in these areas already, and unless I missed something, the recent changes to monster groups and the like should be present and accounted for.

Some new creature symbols were assigned to maintain the kind of "symbol by type" consistency that most of the creatures adhere to.  This means deer now show up as a Nethack-style "q" for quadruped, because "d" is reserved for canids.  This is in line with how we were already displaying "r"odents and "R"obots and other things.  The "q" deer was a little jarring at first, but it's grown on me.  

Some monster types that were previously classed as "UNKNOWN" have a new species ID assigned.  Most of the creature descriptions are rewritten, and a few creature names were changed, although the previous identifiers were left alone for sanity's sake.

The list of new animals for this PR:

- Bat (Vespertilionidae)
- Beaver (Castor canadensis)
- Bobcat (Lynx rufus)
- Bullfrog (Rana catesbeiana)
- Black Rat (Rattus rattus)
- Chicken (Gallus gallus domesticus)
- Cow (Bos primigenius)
- Deer Mouse (Peromyscus leucopus)
- Gray Fox (Urocyon cinereoargenteus)
- Red Fox (Vulpes vulpes)
- Groundhog (Marmota monax)
- Hare (Lepus americanus)
- Horse (Equus ferus caballus)
- Lemming (Synaptomys borealis)
- Mink (Neovison vison)
- Mole (Scalopus aquaticus)
- Muskrat (Ondatra zibethicus)
- Pig (Sus scrofa domesticus)
- River Otter (Lontra canadensis)
- Red Squirrel (Tamiasciurus hudsonicus)
- Sheep (Ovis aries)
- Shrew (Blarina brevicauda) 
- Weasel (Mustela frenata)

Monster group raws were modified as well, the forest group most of all.  Cave populations are less hard-coded, and farm animals will sometimes spawn at abandoned farms, if there are no zombies spawned there.

Also included are normal-sized versions of the giant arthropods.  There's a new VERMIN flag that denotes a creature as too insignificant a size to participate in normal combat or leave behind a corpse.  Vermin are currently always displaced if they player moves into them.  They don't show up on the main screen's list of monsters, and many of them blend in with the ground (at least when using ASCII), so they might not be noticed unless one is actively looking or waiting around in one spot.  

The plan for them is to have vermin sometimes spawn when you pick up rocks and sticks, and to allow the player to eat them by 'e'xamining.  Eating bugs is a very viable survival strategy if you avoid the poisonous ones.  There are also SMALL_BITES and HUNTS_VERMIN flags, but these aren't yet functional.