Use structs to represent parsing keys

[khaledannajar]

I found this feature here in another tool which is putting the parsing keys in a struct for reuse preventing duplication in the keys.
EX.
`private struct SerializationKeys {

static let Id = "Id"

static let timeRange = "timeRange"

}`

This is to be used like this:
`init(fromDictionary dictionary: [String:Any]){

    Id = dictionary[SerializationKeys.Id] as? Int

    if let timeRangeData = dictionary[SerializationKeys.timeRange] as? [String:Any]{

        timeRange = TimeRange(fromDictionary: timeRangeData)

    }

}`

and like this:
`func toDictionary() -> [String:Any]
{
var dictionary = String:Any

    if Id != nil{

        dictionary[SerializationKeys.Id] = Id

    }

    if timeRange != nil{

        dictionary[SerializationKeys.timeRange] = timeRange.toDictionary()

    }

    return dictionary

}`