Provide specification for CSV/TSV

Continued from https://github.com/dosumis/dead_simple_owl_design_patterns/issues/30#issuecomment-305775064

From:
https://docs.google.com/document/d/1xnmLNRMLO7796VmI4GEVv1jadY3e3srLD3gF03h2GqU/edit#heading=h.97ugvf88bemn

Headers:
Defined class: 2 columns: name; or curie.
Named by var: 2 columns per var - name; or curie
String list vars: delimiter should be '|' NOT ','
Override columns:
For name: New column or re-use defined class label column.
Decision: add column: "override label". If filled out, over-rides auto-generated name.
Def: New column
TODO: Add check to prevent re-use of def column name in var.

See also: https://www.w3.org/TR/tabular-metadata/

Start by reading the linked issue 30 comment, the referenced Google document, and the W3C tabular metadata specification. Clarify the CSV/TSV headers, pipe-delimited string lists, override-label behavior, and duplicate-column check; the work is done when these rules are documented as an agreed specification.

Written by the indexing model from the issue text.