Use numbers in module names for better sorting

src/main.rs

@@ -1,6 +1,6 @@
-mod day_one;
-mod day_three;
-mod day_two;
+mod day1;
+mod day2;
+mod day3;
 
 use std::fs::File;
 use std::io::{self, BufRead, BufReader};
@@ -11,12 +11,12 @@ fn main() -> io::Result<()> {
         .lines()
         .map(|line| line.unwrap().parse().unwrap())
         .collect();
-    day_one::main(masses);
+    day1::main(masses);
 
-    day_two::part_one();
-    day_two::part_two();
+    day2::part_one();
+    day2::part_two();
 
-    day_three::main()?;
+    day3::main()?;
 
     Ok(())
 }