- improved interface for chi input
- FE tests for anisotropic chi and negative chi
- Improve internals
- anisotropic susceptibilities are now allowed.
- Improve suszeptibility input possibilities:
- give susceptibility to parent collection
- if susceptiblity input is scalar, isotropic susceptibility is assumed, if it is a 3-vector it can be anisotropic
- Various tests included of interface and computation, isotropic and anisotropic tests confirm computaiton