Defined cli::exit_code, cli::arguments, and cli::environment.
Defined the cli::program class.
Defined the cli::environment class.
Implemented the cli::program#env and #args fields.
Ensured that ./configure checks for the <getopt.h> header file.
Defined the cli::option structure.
Ensured that sizeof(cli::option) equals sizeof(struct ::option).
Ensured that ./configure checks for the getopt_long() function.
Expanded the cli::program constructor to take option definitions.
Ensured that ./configure checks for the getopt() function.
Implemented command-line option parsing in cli::program.
Defined the cli::option_argument enum class.