New Operator oPermutation.

Implicitly represent a permutation operator based
on a permutation vector.
New Operator opFactorization.

Derived class used to represent inverse operators
based on an appropriate factorization. Optionally,
iterative refinement is performed.
New Operator opLU.

opLU represents an inverse operator based on the LU factorization.
New Operator opChol.

opChol represents the inverse of a definite operator based on
the Cholesky factorization.
New Operator opLDL.

opLDL represents the inverse of a real symmetric operator based
on the symmetric indefinite factorization.
Add incomplete LU operator.
Add incomplete Cholesky operator.
Add opQR operator.
Merge branch 'feature/opQR' into develop
Fix for opWavelet2
Incorporated bug fix to products with redundant 2D wavelet transpose.
Minor changes in opWavelet2.m comment section.
Merge of opWavelet2.m and unit tests.