[Nut-upsdev] newhidups: code restructured

[Peter Selinger]

 - newhidups: cleaned up code so that *.h files contain headers, *.c
   files contain sources. Declared all non-exported variables and
   functions as static. Moved code from X-hid.h to X-hid.c, where
   X=mge,apc,belkin. Enclosed all header files in #ifndef/#endif
   pairs.
 - renamed hid-usb.h as libusb.h (since it is the header file that
   goes with drivers/libusb.c)


Note: these changes are contained between before_PSE_5 and after_PSE_5
on the main Development branch. 

-- Peter