Add .NET Core dependencies to nuspec

Updated Changes.txt to prepare for v3.3.3.

Tidied up the SerilogIntegration code.

Updated Changes.txt to cut for 3.3.1

preparing for v3.3 release

updated version to 3.2.2

sigh sigh Sighvelright

bumped up version number to 3.2

updated for v3.1 RTM

fixing .NET 3.5 build