csv-units - add enumeration type
csv-units - move conversion lookup to a dedicated function
csv-units - use name to enum conversion function
csv-units - use enums in the dispatch function
csv-units - create a cast lookup table
csv-units - create a cast lookup table
csv-units - replace the handrafted if-else dispatch code with a lookup table
csv-units - support specifying units fields (but do not use); and fix a bug that stopped conversions working
csv-units - support specifying units fields (but do not use); and fix a bug that stopped conversions working
csv-units - now supports the units being in a data field
csv-units - update units field to the output measurements
csv-units - fix spelling, make --from optional
csv-units - add basic  unit tests - which include units fields in input
csv-units - review cleanup