Doxygen for PAPI_set_debug and minor tweaks to other function documentation.
Doxygen for PAPI_set_debug and minor tweaks to other function documentation.

arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi