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