elastic/elasticsearch-net 2.5.5 on GitHub

Highlights: 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 fields support to top hits aggregations (ty @V1tOr !)

#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)
#2720 Dateformat.epoch_millis serialized a mispelled variant (ty @JefStat !)
#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)