Module macros

Helper macros to ease the declaration of the functions that contain your solutions of the exercises.

• Use [solution!()] to declare a new solution inside of crate::app::Aoc.
• The library currently expects that you want to parse the input. Use either:
  • [failable_parser!()] if the parsing function returns a std::result::Result;
  • [parser!()] if the parsing function returns the plain return value.
• Use [solver!()] to point to the function that solves the exercise.