====== Option +quote_char+

Specifies the character (\String of length 1) used used to quote fields
in both parsing and generating.
This String will be transcoded into the data's \Encoding before use.

Default value:
  CSV::DEFAULT_OPTIONS.fetch(:quote_char) # => "\"" (backslash)

This is useful for an application that incorrectly uses <tt>'</tt> (single-quote)
to quote fields, instead of the correct <tt>"</tt> (double-quote).

Using the default:
  ary = ['a', 'b', '"c"', 'd']
  str = CSV.generate_line(ary)
  str # => "a,b,\"\"\"c\"\"\",d\n"
  ary = CSV.parse_line(str)
  ary # => ["a", "b", "\"c\"", "d"]

Using <tt>'</tt> (single-quote):
  quote_char = "'"
  ary = ['a', 'b', '\'c\'', 'd']
  str = CSV.generate_line(ary, quote_char: quote_char)
  str # => "a,b,'''c''',d\n"
  ary = CSV.parse_line(str, quote_char: quote_char)
  ary # => [["a", "b", "'c'", "d"]]

---

Raises an exception if the \String length is greater than 1:
  # Raises ArgumentError (:quote_char has to be nil or a single character String)
  CSV.new('', quote_char: 'xx')