This is an attempt to fix #86. There are a number of challenges with this new version:

• The download filenames have changed, and require detecting the OS and supporting tarballs.
• Indexes only support 1 document type now, so all indexing and template logic has to reject invalid index configs, and change the wire format.
• Routing during indexing no longer works the same way, the way the test framework does it has been deprecated and removed.

The last part is the only piece that doesn't work. All the test pass except for "should index a document using specified routing", which fails because the _routing metadata key has been removed, and now you can only specify per-document routing inline inside the document. I wasn't sure how to make that work while preserving compatibility with other versions.

That brings me to something else... Compatibility. This library supports 3 major versions of Elasticsearch, 4 with this PR. Elastic very aggressively breaks APIs and compat between major versions, so I had to hack a lot of "oh this is ES7, do something different" into things. I don't think this library format is sustainable for much longer.

I think it would be better to switch to using major versions as well, and following the Elasticsearch major versions: embedded-elastic 6.x supports ES 6.x, embedded-elastic 7.x supports 7.x, ... That way the API can stick to exactly what each version can do, instead of doing the increasingly difficult job of pleasing all of them at once. WDYT?

I think for ES7 the current approach still works, but ES8 will probably break things even more.