elastic/elasticsearch-net 5.4.0 on GitHub

Highlights: Elasticsearch 5.4 feature parity, we are now rolling with the new new csproj files for our builds.

Features & Enhancements

#2717 Moved to the new new csproj file. Which means we are now on VS2017 and up (or Rider of course!). There's a ton of infrastructure cleanup work behind this ticket.
#2659 Add stored_fields support to top hits aggregations (ty @V1tOr !)
#2702 Add support for time_zone in the date range aggregations (ty @adam-mccoy !)
#2746 Add support for missing highlight options as well as new options that have been introduced in 5.4
#2743 Add support for the new remote info API
#2745 Add support for the xpack info AND usage API
#2748 Expose num_reduce_phases on search (see elastic/elasticsearch#23288)
#2747 Expose word delimiter graph token filter
#2744 Add support for the source exists API
#2742 Add support for the field caps API

Bug Fixes

#2753 Timeouts on .NET core did not surface the same way they did as on full framework.
#2735 Do a double read for elasticsearch server errors for requests that can return a valid response for invalid http status codes (_reindex/_update_by_query)
#2740 reintroduce show_term_document_count_error which went blatently missing in 5.x
#2720 Dateformat.epoch_millis serialized a mispelled variant (ty @JefStat !)
#2721 Make sure we can handle fielddata in the old format when mappings are migrated from 2.x to 5.x
#2759 Fix HttpClient when used on CentOS, does not allow maxconnections to be set.
#2761 adjacent scripted metric aggregation responses failed to parse properly (ty @konbur)

For 6.0 we will rely on a new feauture in elasticsearch called typed_keys which will return aggregation names prefixed with type# which will completely replace the current heuristics based parser which should make parsing bugs less likely to creep in. (Although the current one has held up OK since 2.x).