Custom index

CHG   Starting tasks through Task.Factory (recommended TPL pattern)
FIX   Elastic output only took one item at once from the queue rather than clearing it.
ADD   Clients can submit a custom index ("_index" property), which will be used, if available. If not specified, TimberWinR reverts to the statically configured index name, with a fallback to the default index name ("logstash" + date).