adding input and skeleton day4 program

2018/day4/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day4"
+version = "0.1.0"
+authors = ["Andrew Coleman <penguincoder@gmail.com>"]
+
+[dependencies]

2018/day4/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}