Fix for LOGBACK-732, make charset configurable in SyslogAppender

* Add setCharset()/getCharset() methods to SyslogAppenderBase
* Add blurb to news html page
* Unit test

This change change takes the conservative approach of preserving current
behavior when setCharset() is not called, using the platform default encoding.
Merge pull request #194 from noaresare/LOGBACK-732

Fix for LOGBACK-732, make charset configurable in SyslogAppender