Fix l2 plus tests

[bobmyhill]

This PR introduces some breaking changes:

• Renames some functions in utils.math:

  • compare_l2 -> l2_norm_profiles
  • l2 -> l2_norm_profile
  • compare_chifactor -> chisqr_profiles
  • chifactor -> chisqr_profile

  The change in name is both for clarity and, in the case of l2, to encourage the user to recognise that l2_norm and compare_l2_norm now return the true L2 norm, rather than the square of the L2 norm.

• Modifies the parts of the code that used the old functions.

• Removes the following unused functions:

  • float_eq
  • nrmse

• Fixes a small, previously untested bug in complete_basis() in the case where columns were not flipped in the RREF.