Added new writer configuration option 'quoteAll'

[JamesWidman]

Introduces a new encoder option.

Description

Example:

let encoder = CSVEncoder {
  // ...
  $0.quoteAll = true
}

The effect is that each field is quoted in the output regardless of whether it needs to be escaped. This may be useful for round-trip testing where the input file contains redundant quotation marks.

Checklist

The following list must only be fulfilled by code-changing PRs. If you are making changes on the documentation, ignore these.

• [x] Include in-code documentation at the top of the property/function/structure/class (if necessary).
• [x] Merge to develop.
• [x] Add to existing tests or create new tests (if necessary).