Add support for recording and replaying matches

This patch adds support for recording matches (`start --capture`) and replaying recorded matches (`replay replays/last-match.yml`).  Matches are recorded as bot-independent YAML files, so that you can share replays without necessarily sharing the bots that participated.

#### Caveats

The current match is always saved in `replays/last-match.yml`, use the command line to rename files that you don't want overwritten.  If someone wants to improve this, it should be relatively simple.

The replay files get a little large (1.5Mb, 2 bots, 3000 ticks) because I'm using YAML instead of a binary format.  If someone wants to swap the format to improve file sizes, it should be relatively simple.