support durations

[carueda]

Definite syntax still TBD but the idea for the spec would be something like:

durations {
  # optional duration; reported Long (Option[Long] in scala) is null (None) if value is missing
  # or whatever is provided converted to days
  days = "duration:day?"

  # required duration; reported long (Long) is whatever is provided 
  # converted to hours
  hours = "duration:hour"

  # optional duration with default value;
  # reported long (Long) is in milliseconds, either 550,000 if value is missing
  # or whatever is provided converted to millis
  millis = "duration:ms | 550s"
}