Option to print error with causes multiline but no backtrace

[stepancheg]

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 { ... }
}