Add example files

examples/puzzle_game/.gitignore

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+/target

examples/puzzle_game/Cargo.toml

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+[package]
+name = "puzzle_game"
+version = "0.1.0"
+authors = ["Nathan Stocks <nathan@agileperception.com>"]
+edition = "2018"
+
+[dependencies]
+anyhow = "1.0"
+puzzles = { path = "../puzzles" }
+log = "0.4"
+env_logger = "0.8"

examples/puzzle_game/puzzle.dat

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+this is a puzzle

examples/puzzle_game/src/main.rs

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+use anyhow::{Context, Result};
+use log::info;
+use puzzles::Puzzle;
+use std::fs::File;
+
+fn get_puzzle(filename: &str) -> Result<Puzzle> {
+    let fh = File::open(filename)
+        .with_context(|| format!("couldn't open the puzzle file {}", filename))?;
+    let puzzle = Puzzle::from_file(fh).context("couldn't convert data into a puzzle")?;
+    Ok(puzzle)
+}
+
+fn main() -> Result<()> {
+    env_logger::init();
+    let puzzle = match get_puzzle("puzzle.dat").context("Couldn't get the first puzzle") {
+        Ok(p) => p,
+        Err(_) => Puzzle::new(),
+    };
+    info!("Playing puzzle: {}", puzzle.name);
+    Ok(())
+}