Memorial event log

Basic implementation for #2454. Adds a log of events kept on the player that is dumped to the memorial file upon death. It is simply saved and loaded in the .sav file, so you won't lose the log when you save and quit.

I also added a few basic entries to get started, but I encourage others to add more event log statements. It's as simple as:

```
g->u.add_memorial_log("Message", ...);
```

In most cases. In game.cpp you can omit the "g->", and in player.cpp you can omit "g->u.". The function supports varargs. Timestamps and the location are automatically prepended to the message.