Prepare future scaffolding.

Also reformat the code, but that is nothing significant.

2018/src/day25.rs

@@ -0,0 +1,25 @@
+use std::io::Read;
+
+use common::Solution;
+
+#[derive(Default)]
+pub struct Day25 {}
+
+impl Day25 {
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+impl Solution for Day25 {
+    fn part1(&mut self, _input: &mut Read) -> String {
+        unimplemented!()
+    }
+
+    fn part2(&mut self, _input: &mut Read) -> String {
+        unimplemented!()
+    }
+}
+
+#[cfg(test)]
+mod tests {}