Don't skip empty transfers.
Update the fake libusb to honor the endpoint max packet sizes.
Update tests that were taking advantage of the fact that libusb
allowed unlimited amount of data in any transfer packet.
Adds ReadContext/WriteContext methods to endpoints and to streams. Update rawread example tool to use ReadContext for implementation of "timeout" flag.
Defines a WriteStream structure for buffering writes, similar to the existing ReadStream. WriteStreams can be created on OutEndpoints by using ep.NewStream().
* Store a reference to libusb implementation in the context, transfers
and some more places. Remove the global libusb variable.
* Parallelize tests.
* Fix the link in README.
* Add APIs for config and interface descriptors. Split out the common
parts of selecting a config descriptor from device desc and
selecting a setting descriptor from a config desc.
* Parallelize the few tests that actually can be parallelized safely.
Add comments where they can't. Note to self: it would be beneficial
to restructure the fakelibusb to index all properties of the lib
with the used context. That way a libusb implementation wouldn't need
to be referred via a shared variable.
