Implemented creation of edges
Implemented creation of edges

I am quite satisfied with the way (optional) edge weights are being
handled now:

1. If edge weights are available, they are just copied.
2. If not, the weights of the vertices are used.

This has the drawback that in case there are no vertex weights either,
a lot of spurious queries will be made. However, this can always be made
faster for large data sets.

I could provide a different runtime behaviour, for example.

Submanifold/Aleph,Submanifold/Aleph,Submanifold/Aleph