Added Delta sigma data type

[eduardojsbarroso]

When computing the shear profiles for clusters, we can either choose between reduced shear, which might be viewed as the cluster_shear in the standard data types of sacc, or we can use \Delta \Sigma (the excess density surface mass). However there is no way to distinct between these data types and so far we have used the cluster_shear data type for \Delta \Sigma.

So this pull request is just to add this new data_type to sacc.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
1648	1456	88%	0%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
sacc/data_types.py	94%	🟢
TOTAL	94%	🟢

updated for commit: 8df9fd0 by action🐍

[eduardojsbarroso]

@joezuntz This is just one line modification and changed the example notebook. However it would be nice to have this on the sacc version in conda, so we would need a new release. Let me know if this can be merged.