Option to print error with causes multiline but no backtrace

There are for options to print `anyhow::Error`:
* only the message `{}`
* single line causes `{:#}`
* causes and backtrace `{:?}`
* debug `{:#?}`

There's no way to print causes in multiple lines and no backtrace.

Possible API:

```
impl Error {
/// Multiline display: output the message, the causes, but no backtrace even if captured.
pub fn display_no_backtrace(&self) -> impl Display { ... }
}
```