v0.6.1

Code:

• Adds QueryAsync extension to IElasticClient
• Adds new IElasticsearchRepositoryAsync interface and implements on existing ElasticsearchRepository to provide async calls to all existing methods.
• Adds unit tests to cover all async calls
• Removes the additional constructor from ElasticsearchRepository, leaving only the constructor expecting an IElasticClient

Build:

• Moves the build and packaging to Cake
• Alters dependency version graph for Nest from ">=1.6" to ">=1.6 && <= 2.0"