Prevent escaping in xer and jer output

[muued]

Currently the JER and XER encoder escapes non-ascii characters. ISO/IEC 8825-4:2015 clause 8.1.3 and ISO/IEC 8825-8:2015 clause 7.6.2 demand that both outputs should use UTF-8.

Escaping seems to be allowed for XER, but is forbidden in CXER. Escaping seems to be allowed for JER. So, this is probably not a bug.

In my eyes, using the escaping mechanism makes no sense here and leads to less readable output (readability for a human is one of the key features of these encodings). This PR prevents this escaping mechanism.

If for any reason the current behaviour is beneficial, I suggest adding a further parameter (similar to indent) to control the escaping behaviour.