allow public uses of structs; add sample program

src/mock.rs

@@ -67,7 +67,7 @@ pub fn avatar() -> Avatar {
     }
 }
 
-pub(crate) fn sprite() -> Sprite {
+pub fn sprite() -> Sprite {
     Sprite {
         id: "a".to_string(),
         name: Some("hatch".to_string()),
@@ -158,7 +158,7 @@ pub fn room() -> Room {
     }
 }
 
-pub(crate) fn game_default() -> Game {
+pub fn game_default() -> Game {
     Game {
         name: "Write your game's title here".to_string(),
         version: 6.5,