Add rfl::Commented, resolves #597 #511

Job	Run time
windows-msvc-shared (CBOR)	8m 10s
windows-msvc-shared (JSON)	11m 6s
windows-msvc-shared (XML)	3m 42s
windows-msvc-shared (TOML)	4m 11s
windows-msvc-shared (PARQUET)	40m 22s
windows-msvc-shared (CAPNPROTO)	8m 31s
windows-msvc-shared (FLEXBUFFERS)	6m 37s
windows-msvc-shared (UBJSON)	7m 9s
windows-msvc-shared (YAML)	4m 46s
windows-msvc-shared (AVRO)	7m 40s
windows-msvc (FLEXBUFFERS)	6m 5s
windows-msvc (XML)	3m 54s
windows-msvc (TOML)	3m 41s
windows-msvc (JSON)	10m 32s
windows-msvc (CAPNPROTO)	7m 47s
windows-msvc (UBJSON)	7m 6s
windows-msvc-shared (MSGPACK)	7m 22s
windows-msvc (AVRO)	6m 50s
windows-msvc (PARQUET)	41m 11s
windows-msvc (CBOR)	9m 11s
windows-msvc (MSGPACK)	3m 59s
windows-msvc (benchmarks)	46m 35s
windows-msvc (YAML)	4m 25s
	4h 20m 52s

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