Update class.ilCSVWriter.php

[phntxx]

This PR adds a couple of functions to class.ilCSVWriter.php:

• setNewline(string $a_new) allows extending classes to modify the newline character(s) to use, which can prove helpful in some scenarios (e.g. if you require a carriage return (\r) and newline symbol (\n) at the end of a line).
• withXYZ(...) functions allow for one-lined instantation of ilCSVWriter, see the following example.

// before
$writer = new ilCSVWriter();
$writer->setSeparator("a");
$writer->setDelimiter("b");

// after
$writer = new ilCSVWriter()->withSeparator("a")->withDelimiter("b");