CSV(): add support for Ruby 3

[hernanat]

The implementation of the CSV shortcut method is broken in Ruby 3 for calls that look like this:

CSV(write_stream, col_sep: "|", headers: headers, write_headers: true) do |csv|
  ...
end

The above will result in the following error when the CSV method attempts to pass on arguments to CSV#instance:

ArgumentError: wrong number of arguments (given 2, expected 0..1)

The issue is due to the changes in Ruby 3 relating to positional & keyword arguments.

This commit updates the CSV() shortcut implementation to work with Ruby 3, and also updates the documentation for the shortcut method.

[kou]

Thanks!

[hernanat]

thanks @kou !