convert DOK with counts to a list of binary features

given
```py
dok = {(i, j): 123, ..., (j,i): 456}
```

convert to 

```py
pairs = [(i,j, 1), (i,j, 1), ...  # 123x times
              (j,i, 1), (j,i, 1), ... # 456x times
```

@Wuhn 

