Allow events to drop multiple pieces of "fixed" loot

As an example, here's a loot event that will drop 10 gold all the time,
and then either Health Potion (id 1) or a Mana Potion (id 2):

```
currency,5,5,10,fixed;1,5,7,1,100;2,7,5,2,100
```

Note, 0 can be used in place of `fixed`.