Extend NQT output to AthenaK tables

[jfields7]

The NQT module currently only reads and outputs HDF5 files. Getting AthenaK tables (.athtab) has to be done with an external utility (not currently in PyCompOSE, either) to convert HDF5 tables to AthenaK tables. A first step might be porting this utility over, but the second step should be extending the NQT module to read and write AthenaK tables natively.

[dradice]

Yes, please! This is a very useful feature.