std::error::Error extensions

This crate encourages usage of the std::error::Error trait for describing errors, providing the following utilities:

• Error creation: The errors::new, errors::wrap, and errors::opaque functions ease the creation of simple error values.
• Error inspection: Error source chains can be easily iterated with errors::iter iterators to find the error you're looking for.
• Error formatting: The error values created with this crate provide simple yet powerful control over the formatting of errors and their source chains, and the errors::fmt adapter allows foreign error values to follow along.

An Error likely has a message, it might have a cause, and someday, it may have a backtrace. How can a user decide how they should be formatted?

• Top message only

  ship exploded
  

• Top message + message of source chain

  ship exploded: cat hair in generator
  

• Top message + message of source chain + trace/frame

  ship exploded
      at main.rs:55
      at ship.rs:89
  Caused by: cat hair in generator
      at ship::parts::generator.rs:33
      at ship::parts::engine.rs:789
      at ship.rs:89
      at main.rs:55
  

• Default ({}): Print only the top-level message. This is inline with the recommendation for Error
  • Example: println!("top only = {}", err) outputs top only = ship exploded.
  • Alternative: This could also be achieved and possibly clearer by setting the "precision" flag to 0, such as println!("top only: {:.0}", err).
• Message chain ({:+}): Prints the message, and the message of each source, joined by ": ".
  • Example: println!("chain = {:+}", err) outputs chain = ship exploded: cat hair in generator.
• With trace/frame ({:#}): Prints the message and stack trace/frame
  • Example: println!("top trace = {:#}", err) outputs top trace = ship exploded\n at ship.rs:89.
• Message chain with trace/frame ({:+#}): Prints the message and stack trace/frame, and message and trace for each source, joined by \nCaused by:.
• Message chain maximum ({:+.2}): Sets the maximum messages that should be printed down the source chain.