Add a method to the escape tool to encode new line characters in XML attribute values

Since the upgrade to HTML Cleaner 2.5 (XCOMMONS-403) new line characters are not preserved any more in attribute values. For instance, if you write in an HTML form:

<input type="hidden" name="foo" value="$multiLineText" />

on submit, the value of $request.foo will have all new line characters replaced with a space character.

We need a way to encode the new line characters in order to preserve them. Currently the workaround is to replace them like this:

<input type="hidden" name="foo" value="$multiLineText.replaceAll("\n", '&#10;')" />

But more generally, we need to encode the tab \t, the carriage return \r and possibly other white-space characters.