Remove n_ccd=6 as a keyword input argument from the ConstraintTank class.
Add minusz_spec.json. This file definines the parameters for the xija version of the minusz model.
Replace nmass-based ConstraintMinusZ class with xija-based version.
Delete the import of the nmass module.

Signed-off-by: Matthew Dahmer <matthew.dahmer@gmail.com>
Remove nmass.py, remove pars_minusz.json, add minusz_spec.json.
Update version to 0.3.0

Signed-off-by: Matthew Dahmer <matthew.dahmer@gmail.com>
Merge pull request #2 from sot/minusz_to_xija

Convert MinusZ model to Xija framework