use `extern "system"` rather than `extern "stdcall"` (#67)
use `extern "system"` rather than `extern "stdcall"` (#67)

`extern "stdcall"` really only has meaning on x86 Windows; I'm not even sure what calling `extern "stdcall"` functions on x86-64 Windows does (probably bad things?).  `extern "system"` carries the correct meaning on x86 and x86-64 (and other architectures such as AArch64), so let's use that.  (FWIW, `winapi` also uses `extern "system"` for these functions.)
jcjones/u2f-hid-rs,jcjones/u2f-hid-rs