Initial report of OmpSs+OpenACC/OpenMP interoperability

Initial report of the proposed syntax for the combination of OmpSs and accelerator kernels defined with OpenACC and OpenMP syntaxes. Includes semantics and syntax compatibility of OmpSs and OpenACC/OpenMP accelerator kernel definitions, as well as proposals of interoperability improvement for the OpenACC and OpenMP specifications. This is an outcome of Task 3.2.