Move masking/unmasking functions into new masking module

[tsalo]

Summary

We have a handful of masking/unmasking functions that I think should be moved out of utils and into their own module. While I would ultimately prefer to operate mostly on img-like objects (to make it easier for users to call each function in the package without knowing all of the details behind our data loading, masking, unmasking, and data saving procedures), we should move relevant functions out of utils (and potentially io) to reduce bloat in the meantime.

Additional Detail

The functions utils.load_image, utils.make_adaptive_mask, utils.unmask, decomposition._utils.eimask, and potentially io.new_nii_like are all related to masking and/or converting between imgs and arrays. I think that these would be best organized in a masking module.

Next Steps

1. Create masking file (masking.py).
2. Move functions from their current positions to new file.
3. Update imports throughout package.
4. Update tests.
5. Update API organization in docs.

[emdupre]

Sorry, is this instead of #251 ? I'm 👍 on just operating on imgs directly, if that helps in the discussion !

[tsalo]

I was thinking that this would be in addition to that. We’ll be able to eliminate most masking/loading functions but we may want one or two to gracefully apply the masks on the list of imgs. Plus we’ll still have eimask and make_adaptive_mask.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions to tedana:tada: !