Update formatter to sanitize all special characters instead of just quotes

While working on Daphne logging I noticed that newline characters in a log message were breaking the json encoding when using the RabbitOutputter.

I saw this change from several months ago and expanded on it:
https://github.com/mrcrane/log4r/commit/31b8751387545855788391a508a42960af35f202

Instead of only sanitizing quotes, I now use json encoding to escape all special characters including both quotes and newlines. I tested this locally and confirmed that multiline log messages are being parsed correctly by Kibana now.