AppenderDbi             Log to databases via DBI
AppenderDigest          Abstract class for digests (multi-log message
                        notifications)
AppenderDt              Log to an in-memory data.table
AppenderElasticSearch   Log to ElasticSearch
AppenderGmail           Send emails via the Gmail REST API
AppenderMail            Abstract class for email Appenders
AppenderPushbullet      Send push-notifications via RPushbullet
AppenderSendmail        Send emails via sendmailR
AppenderSyslog          Log to the POSIX system log
LayoutDbi               Format log events for output to databases
LayoutElasticSearch     Format log events for output to ElasticSearch
Serializer              Serializers
select_dbi_layout       Automatically select appropriate layout for
                        logging to a database
unpack_json_cols        Unserialize data frame columns that contain
                        JSON
