Remove Support for .NET 3.5
Make .NET 4.5 the target framework
Update NuGet dependencies
Removed post build action (Nuget package build).
Rename projects and restructure folders

`LogentriesCore` becomes `Logentries.Core` and the code has the
appropriate namespace.
Add StyleCop settings
Remove unused references
Merge branch 'feature/StyleCop' into refactor/dotnet45-async
Refactor Logentries.Core to use .NET 4.5 async features