(vc_packager) Multiple volumes import

[maekclena]

Volume options are associated with the last specified slices. For example: vc_packager --volpkg v.volpkg --material-thickness 1000 --name ignored --slices slices1 --name name1 --voxel-size 1 --slices slices2 --name ignored --name name2 --voxel-size 2 is parsed as two volumes: "slices1, name1, 1" and "slices2, name2, 2".

If there is only one slices option, all volume options are associated with it.

Closes #63

[csparker247]

Thanks for this. Just letting you know that it'll be a week or so until I'm able to review it.