Deref for the ErrorKind

Because ChainError implements Deref to &T, we can also match on *e instead of e.kind() or call a function with &e

use crate::chainerror::*;
{{#include ../examples/tutorial12.rs:2:}}
# #[allow(dead_code)]
# mod chainerror {
{{#includecomment ../src/lib.rs}}
# }