update license
add new demo golang_xrender_draw_window_background
move image file to data folder
golang: refactor code, add utils_xgb.go and utils_gdkpixbuf.go
golang: add benchmark test
golang: refactor code
golang: add flags supports, xrender and gdkpixbuf
golang: add gdk_pixbuf c functions
golang: refactor code
golang: add gdkpixbuf functions
golang: refactor code, use *C.GdkPixbuf instead of unsafe.Pointer
golang: add gdkpixbufGetPixbufSize()
golang: refactor code, remove spare c functions
golang: complete doDrawBgByGdkpixbuf()
golang: complete demo
golang: clean code