====== Option +col_sep+

Specifies the \String field separator to be used
for both parsing and generating.
The \String will be transcoded into the data's \Encoding before use.

Default value:
  CSV::DEFAULT_OPTIONS.fetch(:col_sep) # => "," (comma)

For examples in this section:
  ary = ['a', 'b', 'c']

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

Using +:+ (colon):
  col_sep = ':'
  str = CSV.generate_line(ary, col_sep: col_sep)
  str # => "a:b:c\n"
  ary = CSV.parse_line(str, col_sep: col_sep)
  ary # => [["a", "b", "c"]]

Using +::+ (two colons):
  col_sep = '::'
  str = CSV.generate_line(ary, col_sep: col_sep)
  str # => "a::b::c\n"
  ary = CSV.parse_line(str, col_sep: col_sep)
  ary # => [["a", "b", "c"]]

---

Raises an exception if given the empty \String:
  col_sep = ''
  # Raises ArgumentError (:col_sep must be 1 or more characters: "")
  CSV.parse_line("a:b:c\n", col_sep: col_sep)

Raises an exception if the given value is not String-convertible:
  col_sep = BasicObject.new
  # Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
  CSV.generate_line(line, col_sep: col_sep)
  # Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
  CSV.parse(str, col_sep: col_sep)