.NET Standard 1.3 (.NET Core/UWP/UAP support)

[ivanz]

• Framework support:
  • No breaking changes
  • .Net Standard 1.3 (.Net Core, .NET 4.5+, UWP, etc). Only Moq supports .Net standard.
  • .Net 4.0+
  • Tests pass on all frameworks (with mspec 0.10 and mspec.should 0.10 in my private MyGet)
• Adopted new project system (xproj+project.json) to enable the above multi-targeting (also tests run against each framework)
• Moved CI (build, test and packaging) to Appveyor CI and integrated with GitHub
  • Git Tags trigger a publish to NuGet and nuget and assembly verison is controlled in appveyor.yml in the repo.
• CI build pass: Blocked until MSpec 0.10 is out: 0.11.0 Release Plan machine.specifications#308
• Adaptors should have a "package" dependency on Machine.Fakes instead of project
• Publish preview version

Closes: #33
Relates to: machine/machine.specifications#296