2D ropp_io routine 'rationalisation'

[Huw Lewis]

The introduction of 2D background data at ROPP-4 has required new ropp_io read/write, init/free routines to process 2D data, and the introduction of a ROprof2d structure.

Only the Level2b and Level2c elements of the ROprof structure differ between ROprof and ROprof2d. At present, entirely separate routines have been written to process ROprof and ROprof2d, with significant overlap between the two codes.

It is desirable to 'rationalise' the ropp_io code further to provide interfaces to most ropp_io/ropp routines at the 'Level' stage such that the 'master' routines call the required subroutines for the Levels required.

This model is currently followed in routines ropp_io_free and ropp_io_init, but could be extended to all read/write routines.