[Feature Request] Add support to validate values concatenated by __

[Abilityguy]

When values are concatenated by __, lint throws a warning.

For example, when Airport, BusStation and TrainStation are concatenated with __ in
locationOfCrime: Airport__BusStation__TrainStation

the report.json gives

    "level": "LEVEL_WARNING",
    "location": {
      "file": "fbi_hatecrime_stat_vars.mcf",
      "lineNumber": "20923"
    },
    "userMessage": "Failed reference existence check :: value-ref: 'Airport__BusStation__TrainStation', property: 'locationOfCrime'...