AllDays returns all the days in order.

NewDay returns a day which is parsed as a whole initially, and then the parsed data is given to each part.

NewStreamingDay creates a day which takes a parser to convert the input bytes into a stream of inputs, which the part 1 and part 2 functions can then use.

Context is the runner.

Day represents a day of the advent of code.

Part represents a function which given the input will return the answer for that part of the day.