fts-elastic plugin

Hi all, I have recently worked on fts plugin for ElasticSearch. https://github.com/filiphanes/fts-elastic It is forked from fts-elasticsearch as you can see in PR https://github.com/atkinsj/fts-elasticsearch/pull/21 with following changes (maybe some more)

• no duplicate json keys in indexed documents, so compatible with ES 7.x
• 1 elastic index for all users with routing by username
• _id field similar to fts-solr (uid/box_guid/user)
• better json response parsing
• no need to use _source
• added rawlog_dir to config and some more
• renamed all elasticsearch to elastic for shorter names
• fixed http_client leaks
• fixed some compile warnings

I would appreciate if someone with better experience in c and dovecot code would review my code and suggest/push changes.

In my opinion fts-elastic is now functionally on level as currently recommended FTS plugin: fts-solr. I would like to implement proper rescan inspired by fts-lucene so it would become the most complete fts plugin for dovecot.

Filip Hanes