ENH: Add concentration, radius, Delta_Sigma functions to halos module

[sutieng]

Description

This implements several functions to derive the halo concentration, scale radius, the spherical overdensity radius and the excess surface density for halos module.

Checklist

• [x] Follow the Contributor Guidelines
• [x] Write unit tests
• [x] Write documentation strings
• [ ] Assign someone from your working team to review this pull request
• [ ] Assign someone from the infrastructure team to review this pull request

[ntessore]

Hi Sutieng, thank you for your pull request. Could you please set up your git username and email correctly for GitHub? There is a description in the GitHub documentation.

Afterwards, you will need to fix the existing commits in this PR. The easiest that I can think of is resetting your commits without undoing any of the changes, then simply committing again, which will use the new username and email:

$ git reset --soft module/halos
$ git commit
$ git push --force

[sutieng]

Thanks Nicolas! I've just set up the git email and re-pushed all the commits.