This adds a new set of methods to the device class allowing
device objects to be partitioned into multiple sub-devices
using the clCreateSubDevices() function.
For now, device partitioning is only supported on systems
with OpenCL version 1.2 (or later).
This adds support for returning a std::vector<T> from the
various get_info<T>() methods. This provides a simpler
interface to get the values in an array returned from one
of the clGet*Info() functions.
This also adds a test using the new API to get the maximum
work item sizes in each dimension for a device.
