Output to ElasticSearch

[quyse]

• Force all block types to have JSON representation.
• Support for print-schema
• Support for --flat

[quyse]

Done, data can be emitted directly into ElasticSearch instance (--output-elastic http://127.0.0.1:9200/), or dumped into local file (--output-elastic-file test.json) in format suitable for ElasticSearch _bulk request. --continue and --upsert are supported.