allow public uses of structs; add sample program

src/colour.rs

@@ -1,8 +1,8 @@
 #[derive(Debug, Eq, PartialEq)]
 pub struct Colour {
-    pub(crate) red: u8,
-    pub(crate) green: u8,
-    pub(crate) blue: u8,
+    pub red: u8,
+    pub green: u8,
+    pub blue: u8,
 }
 
 impl From<String> for Colour {