The focus of this PR is mostly on tests and docs, although there are a few other bits as well.
The main highlight is added support for the latest version of Elasticsearch - 7.1.x
[Travis] Replaced elasticsearch deb package with a docker image of elasticsearch. It is simpler to run, no need to maintain the list of download files and the tests don't take any longer after the change.
[Travis] Added tests for the highest three minors in the 6.x line and the highest two minors in the 7.x
[Unit] Added missing tests for $missing and $exists
[Service] Added support for 7.x line - the pagination needed to take into account that total in 7.x is return as an object rather than a number.
[Docs] Added description of the whitelist option. Added "Contributing" section.
Summary
The focus of this PR is mostly on tests and docs, although there are a few other bits as well.
The main highlight is added support for the latest version of Elasticsearch - 7.1.x
$missingand$existstotalin 7.x is return as an object rather than a number.whitelistoption. Added "Contributing" section.