event callback directly using object pointer

pyopencl/_cffi.py

pyopencl/c_wrapper/wrap_cl_core.h

pyopencl/cffi_cl.py

src/c_wrapper/error.h

src/c_wrapper/pyhelper.cpp

src/c_wrapper/pyhelper.h

src/c_wrapper/utils.h

src/c_wrapper/wrap_cl.cpp