Minor feats

[maximelucas]

Implements #183 and #184.

[leotrs]

@nwlandry recently we discussed making num_edges a method instead of a property - do you remember what was the context of that? If we ever get to that, then we might as well just add the order parameter to num_edges instead of adding a second method like on this PR.

[nwlandry]

I believe that this was in the context of simplicial complexes where there are different notions of number of simplices (i.e., is it all the subfaces as well, or just maximal simplices?)