Add more typecasts for Windows`

This is based on an older patch by Lubomir I. Ivanov <neolit123@gmail.com>
which no longer applies due to the refactoring of the registry setting
code.

It takes care of all of the casts between actual C types and the Windows
specific types that the Windows API functions expect. It also adds some
comments to the overloading of "value" in our subsurface_set_conf function.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>