Support single rolls in various rolls

While running this works:
```
hxgm30 roll meta d6 10 d4 4 d20 2 d100 1
```
this does not:
```
hxgm30 roll d6 10 d4 4 d20 2 d100 1
```

In particular, the non-meta code doesn't know how to handle a single roll of a die that is part of a series of various rolls.