Add an `errors` example that creates and prints various error types from
the crate. This is useful for two main purposes:

- Helps us catch mistakes by exercising error paths.
- Helps us check that error output is useful for debugging.
- Helps us check that output for "alloc" builds is good/useful (no-std)

Run with appropriate features to verify the output, e.g.,

  `cargo run --example errors --no-default-features --features=alloc`

Remove the 'code=' and just write the character in single quotes.