JSON5 support, and comprehensive tests and examples

[konklone]

This pull request:

• Adds support for JSON5, while retaining support for other JSON variants.
• Adds test examples (with JSON input and CSV output) for each documented kind of supported JSON variant.
• Removed my own crude regex-based support for unquoted keys (now done by JSON5).
• Removed my own crude regex-based approach to removing smart quotes (this appears no longer unnecessary).

This means we now support:

• JSON, using the browser's native JSON.parse() function
• JSON5, using the JS-based JSON5 parser distributed at json5/json5. (Provides support for inline JS comments, unquoted keys, single-quoted keys and strings, line breaks inside strings,, trailing commas, positive + signs on numbers -- see below.)
• JSON Lines, a special format which allows one-JSON-object-per-line. This is done using crude regexes on my part.
• A trailing comma at the end of the JSON input. Done using a crude regex on my part.

For an example of what JSON5 supports, this is the canonical example from their README:

{
  // comments
  unquoted: 'and you can quote me on that',
  singleQuotes: 'I can use "double quotes" here',
  lineBreaks: "Look, Mom! \
No \\n's!",
  hexadecimal: 0xdecaf,
  leadingDecimalPoint: .8675309, andTrailing: 8675309.,
  positiveSign: +1,
  trailingComma: 'in objects', andIn: ['arrays',],
  "backwardsCompatible": "with JSON",
}

Putting the JSON5 example above into the JSON-to-CSV converter (as of this PR) parses this as expected and renders it:

All tests produce the expected output.