better message for httptransfer exceptions
upgraded shift-it with better exception messages
Fixed corner cases around headers.

Adding Accept, Accept-Encoding, adding a value multiple times.
Setting a Host header will now result in the expected behaviour.
Request and response headers are now case-insensitive, as per RFC2616.
NuGet in VS now has a proper working restore, so no need to keep the binaries in the repository.
NuGet package generation instructions.