v3.0.0

Major version bumped to 3, targeting net45.
Upgraded the whole solution to Visual Studio 2017.
Combined JWTAuth code, no need for Box.V2.JWTAuth any more.
Added Recents API support.
New operations on Metadata API.
External App User ID: Apps can now store any unique external identifier for an app user which can be used to search for an app user.
Progression support on UploadUsingSessionAsync.
Other minor fixes/improvements.

https://www.nuget.org/packages/Box.V2/3.0.0
https://www.nuget.org/packages/Box.V2.Core/3.0.0