#80 Escape CR in Strings util class

[Marco Krikke]

ical4j escapes CRLF and LF line endings to \n. However, single CRs are not escaped. The single CR is preserved in the iCalendar output, resulting in a files that is unparsable by clients.

A common scenario for this is when users copy data from Excel to SQL Server Management Studio, when for some reason newlines are copied as CRs (blegh).

Please find attached a patch that escapes CRLF, LF and CR line endings.