Allow iterating over object keys

[lsmacedo]

Example object:

"bpi": {
  "USD": {
    "code": "USD",
    "symbol": "$",
    "rate": "29,911.4932",
    "description": "United States Dollar",
    "rate_float": 29911.4932
  },
  "GBP": {
    "code": "GBP",
    "symbol": "£",
    "rate": "23,800.9640",
    "description": "British Pound Sterling",
    "rate_float": 23800.964
  },
  "EUR": {
    "code": "EUR",
    "symbol": "€",
    "rate": "27,997.2174",
    "description": "Euro",
    "rate_float": 27997.2174
  }
}

We should be able to iterate through each key as a row and get their values.

Suggestion:

"alias": {
  "_currency": "_.bpi__*__"
},
"tables": {
  "currency": {
    "set": {
      "name": "_currency.code",
      "label": "_currency.description",
      "rate": "_currency.label"
    }
  }
}