As the name already indicates, a device descriptor is lightweight
object which describes a single device. Currently, the api supports
getting the device name (vendor and product) and model number. But
this can extended with other features when necessary.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.
