Added Character Combat Use Cases

Ended up breaking Character Combat into two use cases, one involving both players and one when the phase player is just fighting a creature or irate locals. This is because both cases required enough variation in what actor performed what task that I felt it was necessary. Obviously open to ideas for changes and feedback!

Also wasn't sure if we were putting all the use cases in separate TeX files or not, but since I saw pre-game was also added to the missions file then I assumed we were just going for one.