Solutions in Rust by David Szotten
Each day is a separate binary:
$ day01 --help
adventofcode
USAGE:
day01 [OPTIONS] <input>
FLAGS:
-h, --help Prints help information
-V, --version Prints version information
OPTIONS:
-p <part> [default: 1] [possible values: 1, 2]
ARGS:
<input> Sets the input file to use, or `-` for stdin