implement RFC #77 (module reflection)

[weyrick]

see #77

[rboucher-me]

The RFC needs to be revisited and updated.

[leoparente]

C++ does not support reflection by standard. It still a proposal. We should discuss the better way to achieve that RFC.

Some C++ reference libs: Boost.PFR Cereal refl-cpp

[weyrick]

yes to be clear this is not C++ code level "reflection", it's just a way for pktvisor to self-describe and document the handler capabilities, configuration, metrics, metric groups, etc.