Include caller info to false by default
Read custom JSON fields from configuration
Added customs json fields
Unit test for news json custom fields
updated documentation for custom fields and syslog appender
Merge branch 'add-field' of https://github.com/braoru/logstash-logback-encoder into braoru-add-field

Conflicts:
	README.md
	src/main/java/net/logstash/logback/LogstashFormatter.java
	src/main/java/net/logstash/logback/encoder/LogstashEncoder.java
Update .gitignore