Compress multiple rows of sometimes-misaligned headers into one

[DavidGinzberg]

From source:

...
#TODO: Add option to compress multi-line categorical headers (eg: headers with colspan>1) into concatenated-naming-style single row headers
#  EG: "Population" header spanning above sub-headers "Number" and "Percentage" produces two single-column headers of "Population - Number"
#  and "Population - Percentage". Delemiter can be configurable with a sensible default set.
...

IIRC the CSV spec only allows for one line of headers, so this is also a specification compliance issue.

[DavidGinzberg]

The current implementation works against this pretty hard. It would probably be easier to address this after refactoring to a more object-oriented or functional approach.