Stop linking the kernel driver into PawnIOLib

PawnIOLib linked the PawnIO target purely to inherit its include directory,
and the driver's own dependencies were declared with the implicitly-PUBLIC
target_link_libraries signature, so ntoskrnl.lib, hal.lib, wmilib.lib,
bufferoverflowfastfailk.lib and ksecdd.lib all propagated into a user-mode
link. It resolved correctly only because ntdll.lib happened to be listed
first -- ntoskrnl.lib exports NtClose, NtDeviceIoControlFile and
RtlNtStatusToDosError too, so reordering the list would have produced a DLL
importing from ntoskrnl.exe, which cannot load.

Split the public headers into a PawnIOInclude interface target and link that
instead.