Implemented the switch --mirror.

When this switch is used, then mirror images are considered to be distinct.

This resolves #5.
Fixed part of the issues with --relabel switch.

This is part of the solution for #6, but there are still some other problems.
Fixed part of the issues with --relabel switch.

The degrees were not moved, so the array degree contained wrong degrees for several vertices.
This is part of the solution for #6, but there are still some other problems.
Fixed part of the issues with --relabel switch.

The degree for vertex 0 was not set, so this contained a random value.
This last commits appears to resolve #6.