Inconsistency between javadoc and code

[Line 118](https://github.com/viskan/logstash-appender/blob/master/src/main/java/com/viskan/log4j/logstash/appender/LogstashAppender.java#L118) states that parameters are comma-separated but the [processing code on line 71](https://github.com/viskan/logstash-appender/blob/master/src/main/java/com/viskan/log4j/logstash/appender/LogstashAppender.java#L71) does a split by '&'.