Poor error when template file is not found

[dtolnay]

The Debug representation of errors is typically not designed to be shown to users.

#[derive(Template)]
#[template(path = "ello.html")]
struct HelloTemplate<'a> {
    name: &'a str,
}

error: proc-macro derive panicked
 --> src/main.rs:7:10
  |
7 | #[derive(Template)]
  |          ^^^^^^^^
  |
  = help: message: called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "No such file or directory" } }