Umbrellas

This adds an umbrella item that helps keep you dry and protect you from rain when it is wielded.

This PR also:
* Adds umbrellas/raincoats to a few appropriate spawn lists.
* Small tweaks to acid rain/drizzle effects; drizzle is slightly more harmful, rain is the same but has a more smooth effect instead of causing pain to jump larger amounts
* Buffs raincoat chances of blocking acid rain/drizzle, wearing a raincoat and wielding an umbrella will actually block a fair amount of acid rain's effect, and most of an acid drizzle's effect.
* Adds a small chance for normal rain to penetrate a raincoat/umbrella. This effect is small enough that the morale penalty usually never goes above a 1-3.