log4stash 2.1.0

• Change request's content type to support newer version of Elasticsearch

• Supports Elastic Cloud indexing

• Closed issues:
  ** #30 Update request content type
  ** #34 Add getters for IndexName and IndexType fields
  ** #40 Error 406 with ElasticSearch 6.0 RC 2

• Merged pull requests
  ** #31 Add routing option
  ** #32 Add IndexOperationParams
  ** #37 Add config option if elastic is not in the root path
  ** #41 Changed the way to determine if response contains an error

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

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