Rebase to libusb/connection-callback

[andyvorld]

PR to rebase device_notify onto the new https://github.com/libusb/hidapi/tree/connection-callback.

Mainly a straight copy + paste job to get the minimal example to compile, and two modifications.

• In interface_notify_callback, the device path is no longer normalized and uses hid_internal_UTF16toUTF8 instead of wcstombs
• In hid_hotplug_deregister_callback hotplug_cb->handle was changed to (*current)->handle to address a nullptr access from Add hotplug support libusb/hidapi#238 (comment).

[Youw]

please resolve conflicts - otherwise it will be impossible to merge anyway

[andyvorld]

I thought it would be a reset to my branch's head? As the device_notify branch was rebased so there are no easy common ancestors.
I can still try to resolve the conflicts if its meant to be merged in.

[DJm00n]

@andyvorld thank you for your work. I have manually rebased my changes under current upstream/master branch and also cherry-picked your b864213 fix.
Also, your 80e3e01 change was a bit broken - so I did proper changes instead while rebasing.

I've done this to avoid unnecessary noise in the git history.