coap_config.h.windows:
Windows has struct cmsghdr so use it.
Update libcoap versions.
include/coap2/coap.h.windows:
Update libcoap versions.
Bring in line with build include/coap2/coap.h.
include/coap2/coap_session.h:
Include coap_forward_decls.h so things build correctly.
win32/libcoap.vcxproj:
win32/libcoap.vcxproj.filters:
Add in missing include files.