This internal function will export each qw field of a given data frame
to separate columns in a single comma separated file (csv). The left header information
will be used "as is" but the data fields will be named with the qw column name
and the qw slot names .Data.values, .Data.value2, and remark.codes (e.g., secchi..Data.values).
These slots names will be renamed _lo, _hi, _symbol (e.g., secchi_lo).
The remaning qw slot values will not be exported.
The exported file will be in a directory specified by the user (defaults to working directory).
The file will be named as specified by the user.