Added rfl::DefaultVal, resolves #534 #366

Job	Run time
windows-msvc-shared (JSON)	10m 17s
windows-msvc-shared (AVRO)	7m 38s
windows-msvc-shared (CBOR)	9m 29s
windows-msvc-shared (FLEXBUFFERS)	5m 43s
windows-msvc-shared (MSGPACK)	3m 58s
windows-msvc-shared (CAPNPROTO)	7m 43s
windows-msvc-shared (PARQUET)	40m 8s
windows-msvc-shared (YAML)	4m 19s
windows-msvc-shared (XML)	4m 28s
windows-msvc-shared (UBJSON)	7m 56s
windows-msvc-shared (TOML)	5m 8s
windows-msvc (UBJSON)	7m 18s
windows-msvc (PARQUET)	32m 42s
windows-msvc (CBOR)	8m 35s
windows-msvc (benchmarks)	32m 40s
windows-msvc (JSON)	10m 36s
windows-msvc (TOML)	3m 43s
windows-msvc (FLEXBUFFERS)	6m 10s
windows-msvc (YAML)	4m 27s
windows-msvc (AVRO)	7m 19s
windows-msvc (XML)	3m 58s
windows-msvc (CAPNPROTO)	7m 52s
windows-msvc (MSGPACK)	3m 46s
	3h 55m 53s

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