for 1.0
=======
cancellation race concerns - better tracking of kernel feedback?
isochronous endpoint I/O
thread safety
error codes
fixme review
review functionality missing over 0.1
endianness of control setup, issues when resubmitting transfers
rename poll to handle_events
make libusb_get_pollfds return const?
doxygen warnings
make descriptor things const?

1.0 API style/naming points to reconsider
=========================================
typedef _cb or _cb_fn or _cb_t?
typedef as-is or pointers? libusb_dev_t rather than libusb_dev *?

for 1.1 or future
==================
optional timerfd support (runtime detection)
notifications of hotplugged/unplugged devices
use poll() rather than select()?
offer API to create/destroy handle_events thread