Rewrite old code into 2018 style.

Nice test for my 2018 repo set up. Which turns out needs some tweaking.

2016/src/main.rs

@@ -0,0 +1,65 @@
+extern crate clap;
+use clap::{Arg, App};
+use std::fs;
+use std::io;
+
+pub mod common;
+pub mod day1;
+
+fn get_impl(day: i32) -> Box<common::Solution> {
+    match day {
+        1 => { Box::new(day1::Day1::new()) }
+        _ => {
+            panic!("Unimplemented day {}", day)
+        }
+    }
+}
+
+fn main() {
+    let matches = App::new("Advent of Code")
+        .version("2016")
+        .author("Bert Peters <bert@bertptrs.nl>")
+        .arg(Arg::with_name("day")
+             .value_name("DAY")
+             .help("Number of the day to execute")
+             .required(true)
+             .takes_value(true))
+        .arg(Arg::with_name("part2")
+             .short("2")
+             .help("Whether to run part 2")
+             .long("part2"))
+        .arg(Arg::with_name("input")
+             .short("i")
+             .long("input")
+             .help("Optional input file, stdin otherwise")
+             .takes_value(true))
+        .get_matches();
+
+    let day: i32 = (&matches.value_of("day").unwrap()).parse()
+        .expect("Invalid int");
+    let mut implementation = get_impl(day);
+    let mut data: Box<io::Read> = match matches.value_of("input") {
+        Some(filename) => { Box::new(fs::File::open(filename).unwrap()) }
+        None => { Box::new(io::stdin()) }
+    };
+
+    if matches.is_present("part2") {
+        println!("{}", implementation.part2(&mut data));
+    } else {
+        println!("{}", implementation.part1(&mut data));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_get_impl() {
+        // Verify that we can load all days
+        let last_implemented = 1;
+        for d in 1..(last_implemented + 1) {
+            get_impl(d);
+        }
+    }
+}