This closes issue #293

This fixes issue #287

This fixes issue #278.

Use int64_t instead of int32_t as the default label type.

This introduces support for returning a generator in
subgraph_isomorphism(), so that all matches do not need to be kept on
memory simultaneously.

This fixes issue #255.

Improve slightly the performance of shortest_distance() with multiple targets and revert shortest_path() to single-target-only

This fixes #192

This also properly handles self-loops and thus fixes #180.

This fixes #176.

This replaces a custom implementation of Ullmann's code.