Added high-level building instructions
Fixed the code blocks in the README
Added more info to README
Added DamageKey and stub for damage resolution

Entities can communicate what kind of damage they deal and take through
their damage id.
Added damageId to Weapon and associated classes

In order to allow damage lookups the damage ID needed to be added to
associated classes.
Merge pull request #95 from zackthehuman/master

First pass at adding damage to different components