log4stash 2.2.1

• Supporting .net core 2.

• Using RestSharp for the ElasticClient instead of legacy code.

• Update content-type in aws signing code.

• Closed issues:
  ** #26 Make compatible with .NET Core
  ** #40 Error 406 with ElasticSearch 6.0 RC 2
  ** #47 Remove (Begin/End)GetRequest async mechanism

• Merged pull requests
  ** #42 Updated the nuspec to support .net core 2.0
  ** #48 Replaced WebRequest with RestSharp
  ** #49 update content-type in aws signing code to application/json for ES 6.0

Thanks a lot to @erangil2 for his tremendous contributions :)

And thanks to: @zhengziying, @triarc, @prime8, @henkish, @mfpalladino, @ignasv, @wpgh, @Thecentury and @pnumainville for their contributions.