rust book again

.gitignore

@@ -5,6 +5,7 @@
 /arduino/arduino.mk
 /arduino/libraries/*
 /arduino/libraries/.raw/
+/hello_world/main
 /oldstuff/intro-to-crafty/assets/*
 /oldstuff/intro-to-crafty/lib/crafty.js
 /oldstuff/intro-to-crafty/tmp/*

hello_world/main.rs

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