Uniform params for get_multi_paths

Hi all, I think wouldbe great, just to have an easier way to use the functions, adjust the params of ```get_multi_paths``` for the same as the others.

```get_multi_paths<-function(Graph, from ,to ,keep=NULL, long=FALSE)```

Ideally add the ```algorithm``` param, with the one that supports:
```get_multi_paths<-function(Graph, from ,to ,keep=NULL, long=FALSE, algorithm = "Dijkstra")```

Thx!