Fix c++ and windows compatibility

[sshsphere]

Add explicit casts and use Sleep function instead of nanosleep on windows

[nathhB]

It fails to compile:

In file included from /Users/nathb/Dev/GameDev/nbnet/soak/client.c:37:
/Users/nathb/Dev/GameDev/nbnet/soak/../net_drivers/webrtc_c.h:325:65: error: expected expression
    struct json_object_element_s *curr = (json_object_element_s*)object->start;
                                                                ^
/Users/nathb/Dev/GameDev/nbnet/soak/../net_drivers/webrtc_c.h:325:43: error: use of undeclared identifier 'json_object_element_s'
    struct json_object_element_s *curr = (json_object_element_s*)object->start;
                                          ^
/Users/nathb/Dev/GameDev/nbnet/soak/../net_drivers/webrtc_c.h:422:31: error: unexpected type name 'rtcConfiguration': expected expression
    rtcConfiguration rtcCfg = rtcConfiguration{
                              ^
/Users/nathb/Dev/GameDev/nbnet/soak/../net_drivers/webrtc_c.h:461:41: error: unexpected type name 'rtcDataChannelInit': expected expression
    rtcDataChannelInit rtcDataChannel = rtcDataChannelInit{
                                        ^
4 errors generated.
make[2]: *** [CMakeFiles/client.dir/build.make:76: CMakeFiles/client.dir/client.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:85: CMakeFiles/client.dir/all] Error 2
make: *** [Makefile:91: all] Error 2