Resolve clippy::must_use_candidate warnings

- See https://rust-lang.github.io/rust-clippy/master/index.html#must_use_candidate

src/bin/scaffold.rs

@@ -8,10 +8,12 @@ use std::{
     process,
 };
 
-const MODULE_TEMPLATE: &str = r###"pub fn part_one(input: &str) -> Option<u32> {
+const MODULE_TEMPLATE: &str = r###"#[must_use]
+pub fn part_one(input: &str) -> Option<u32> {
     None
 }
 
+#[must_use]
 pub fn part_two(input: &str) -> Option<u32> {
     None
 }

src/lib.rs

@@ -41,6 +41,7 @@ macro_rules! solve {
     }};
 }
 
+#[must_use]
 pub fn read_file(folder: &str, day: u8) -> String {
     let cwd = env::current_dir().unwrap();
 
@@ -54,6 +55,7 @@ fn parse_time(val: &str, postfix: &str) -> f64 {
     val.split(postfix).next().unwrap().parse().unwrap()
 }
 
+#[must_use]
 pub fn parse_exec_time(output: &str) -> f64 {
     output.lines().fold(0_f64, |acc, l| {
         if l.contains("elapsed:") {