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.

[codecov]

Codecov Report

Merging #158 (12f34ca) into master (349e9a7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #158   +/-   ##
=======================================
  Coverage   35.18%   35.18%           
=======================================
  Files           7        7           
  Lines        8567     8567           
=======================================
  Hits         3014     3014           
  Misses       5553     5553           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[coveralls]

Coverage: 96.47%. Remained the same when pulling 12f34ca on muued:master into 349e9a7 on eerimoq:master.