alpaka3-tuner

move alpaka_finalize out of function scope (some variables may be dropped or changed in scope as cuda has problems verifying language properties)

add Info struct allowing the user to view the current tuning state of a tuning context, add readthedocs setup

add SessionSpecs - which is a holder for runtime session specifiers -- allowing per session specific break criteria in addition to contextSpecifier(restrict tuning context)

add alpakaTune_finalize (wrapper for alpaka_finalize) -- make alpakaTune::alpakaTune indepedent interface (not hijacking alpaka cmake namespace)

Initial commit based on previous alpaka3 fork for the alpakaTuner.