amqp implementation

example configuration:

log4j.appender.graylog2.amqpURI=amqp://user:pw@host:port/%2F
log4j.appender.graylog2.amqpExchangeName=graylog.gelf
log4j.appender.graylog2.amqpRoutingKey=#
log4j.appender.graylog2.amqpMaxRetries=5
log4j.appender.graylog2.facility=test-application
log4j.appender.graylog2.extractStacktrace=true
log4j.appender.graylog2.addExtendedInformation=false