.NET Core 1.0 compatible release

This is the first 2.x release that uses the new .NET Core 1.0 RTM release in conjunction with the latest dotnet tooling (1.0.0-preview2-003121). Included frameworks

• .NET 4.5 (net45)
• .NET 4.6 (net46)
• .NET Standard 1.3 (netstandard1.3)

The dependency on Json.NET in NEST has also been updated to major version 9.0.0

Massive thanks to @phenixdotnet for the initial PR to move the projects over from using dnx and .NET Core RC 1 dependencies 👍

Bug Fixes

• #2145 Add size to source when using the ReIndex API