Enable cargo run and use this to run all solutions.

2020/src/lib.rs

@@ -1,9 +1,9 @@
-mod day1;
-mod day2;
-mod day3;
-mod day4;
-mod day5;
-mod day6;
+pub mod day1;
+pub mod day2;
+pub mod day3;
+pub mod day4;
+pub mod day5;
+pub mod day6;
 
 use aoc_runner_derive::aoc_lib;