CCD and CDD general-index operators implemented and partially tested with c2, h2o, H2O
general CCD, CDD, CDC operators built and tested with c2, h2o and H2O at 2PDM level.  Seems to work, but don't fully understand use of transpose/commute/PARITY factors
basic structures for 3pdm arrays and routines implemented; next need to finish antisymmetry, spin to non-spin, spin to spatial transformations
forgot a file