Add EntityFramework.Testing.NSubstitute.csproj

- Added NSubstituteDbSetExtensions.cs
Add EntityFramework.Testing.NSubstitute.Tests.csproj

- Added ManipulationTests.cs
- Added QueryTests.cs
Update copyright comments
Updated EntityFramework.Testing.NSubstitute

- Updated StyleCop statements for:
  . ManipulationTests.cs
  . QueryTests.cs
  . NSubstituteDbSetExtensions.cs

- Simplfied callback methods for Add, AddRange, Remove and RemoveRange
Update NSubstituteDbSetExtensions

- Avoid enumerator modification exception
Update README.md
Add NuSpec for EntityFramework.Testing.NSubstitute
Update NuGet builder batch