heterodyne:  Derive and record the baseline noise (RMS_MAP).

This is calculated after masking of the emission and trimmed noisy ends.
heterodyne: Store the array RMS to the Frame's internal header.

This is for the noise-statistics log.
heterodyne: New primitive to collate and log the noise statistics.
heterodyne: Check whether SURVEY_HEADER is defined.
heterodyne: Pass SURVEY_OVERRIDE to _QA_TIMESERIES_CHECK_.

This is part of the requirements to perform Legacy-survey QA checks
rather than those of the original survey.
general: Tidy spacing and avoid long command lines.
general: Add comment to explain reason for quotation marks in FITSMOD.
heterodyne: Add POD markup.
heterodyne: Write to new noise-statistics log.

The new primirtive is called after every occurrence of
_QA_WRITE_REPORT_.
heterodyne: Use filename markup.