csvjoin: Join two CSV files

[Notgnoshi]

This will need research. Probably use qsv as a reference.

Use-cases:

• Append a new column (one-to-one row correspondence)
• Append a new column (interleave rows, requires sharing a common column, and defining how gaps should be left/filled)
• Interleave new rows (either concatenate (easy) or interleave with a common column, like an index or a timestamp)