Include swiftshader folder in NuGet packages

[merceyz]

Changes:
Include the swiftshader folder and its DLLs in the NuGet packages

Resolves #58

[perlun]

Nice, thanks! Merging.

[amaitland]

Additional changes are required to support swiftshader, adding the files to the package isn't enough to get them copied to the target build folder. Restructured the packages so all files and folders are included now.

See commit 18b9d74

Additional changes will be required to CefSharp, they'll follow in a bit.

[perlun]

Nice changes @amaitland, thanks! Yeah, it's better to include *.dat etc rather than a fixed list, much more forward-looking that way.