hid_error implementation for libusb

[Youw]

• hid_error is set correctly for most of the API functions (except hid_enumerate/hid_open/etc.);
• refactored iconv routines - common code for utf16 and utf8 to wchar_t implementation;
• hid_libusb_error to have libusb error code when possible;

Closes: https://github.com/libusb/hidapi/pull/690 Fixes: https://github.com/libusb/hidapi/issues/684

Co-authored-by: Matheus Afonso Martins Moreira [email protected]

[Youw]

Still need to implement global error.