Parsing simple HTTP headers using pre-defined header descriptions.
Examples:
letresponse=HTTPURLRseponse(..., headers:["X-RateLimit-Reset":"2015-01-01T00:00:00Z"])letheader=HTTPHeader<Date>(field:"X-RateLimit-Reset")letdate=try header.parse(from: response)
// let date = try header.parseIfPresent(from: response)