edgeBleach can have 'duplicate' keys

```
import theseus as th
edge_list = [(0,1,0,0),(1,0,1,1)]
d = th.edgeBleach(edge_list)
print(d)
```
output
```
{(0, 1): [(0, 0)], (1, 0): [(1, 1)]}
```

it should output
```
{(0, 1): [(0, 0),(1, 1)]}
```

gave me a bug when plotting because it drew one edge over the other