Finalize exponent support in weighting
Finalize exponent support in weighting

- Add exponent argument to free functions
- Update documentation regarding exponents
- Fix inconsistent implementation of inf-norm
- Fix validity check for matrices and add corresponding vector check
- Restrict singleton pattern to the standard case in no-weighting case

aringh/odl,odlgroup/odl,kohr-h/odl,kohr-h/odl,odlgroup/odl,aringh/odl