This changes the BOOST_COMPUTE_FUNCTION() macro (and the related
BOOST_COMPUTE_CLOSURE() macro) to use custom, user-provided argument
names instead of auto-generating them based on their index.
This is an API-breaking change. Users should now provide argument
names when using the BOOST_COMPUTE_FUNCTION() macro. The examples
and documentation have been updated to reflect the new API.
This adds a new macro to ease the definition of custom user
functions. The BOOST_COMPUTE_FUNCTION() macro creates a new
boost::compute::function<> object with the provided return
type, argument types, function name and OpenCL source code.
