Deprecate vol2img #265
Description
Following #231, the usage of vol2img will be reduced to it's own unit test and generation of imgs_clean in test_covar2d.py. Other cases have been replaced by Volume.project. However, this case I had trouble reproducing. I probably wasn't using it correctly, but if I was this may require some care and regeneration of test data.
Following that vol2img should be totally removed.