Add built-in support for CSV/TSV

[webketje]

Use case:

Excel/Google sheet worksheets saved as CSV/TSV

• Use https://www.npmjs.com/package/csv-parse as optional peerDependency (similar to toml implementation)
• CSV can be parsed either as array of arrays or array of objects. A CSV is not guaranteed to have a header row so array of arrays is safer.
• will require being able to specify options at some point (breaking change with current)