Allow Compare and Allocator on map-like data structures; resolves #561 #497

Job	Run time
windows-msvc-shared (CBOR)	8m 30s
windows-msvc-shared (CAPNPROTO)	8m 41s
windows-msvc-shared (JSON)	11m 49s
windows-msvc-shared (XML)	4m 3s
windows-msvc-shared (TOML)	4m 4s
windows-msvc-shared (AVRO)	7m 35s
windows-msvc-shared (MSGPACK)	4m 45s
windows-msvc-shared (UBJSON)	8m 22s
windows-msvc-shared (YAML)	4m 8s
windows-msvc-shared (FLEXBUFFERS)	5m 39s
windows-msvc-shared (PARQUET)	40m 57s
windows-msvc (CBOR)	8m 12s
windows-msvc (YAML)	4m 58s
windows-msvc (TOML)	7m 17s
windows-msvc (FLEXBUFFERS)	5m 50s
windows-msvc (benchmarks)	51m 3s
windows-msvc (AVRO)	8m 11s
windows-msvc (MSGPACK)	4m 10s
windows-msvc (CAPNPROTO)	7m 50s
windows-msvc (XML)	4m 31s
windows-msvc (PARQUET)	39m 44s
windows-msvc (JSON)	11m 4s
windows-msvc (UBJSON)	8m 19s
	4h 29m 42s

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