CSV dialect schema and spec

[roll]

http://specs.frictionlessdata.io/csv-dialect/ https://github.com/frictionlessdata/schemas/blob/master/csv-dialect-description-format.json

If I've got it right the spec says nothing about required/not required fields. In my opinion all fields could be optional so even not sure schema is useful here.

cc @akariv

[danfowler]

@roll I think you're right. All fields could be optional because all fields have defaults. However, the csv-dialect-description-format.json could still be useful to check for misspellings in property names, but only if we add "additionalProperties": false.