[FEATURE REQUEST] Add ability to bail! and ensure! error types.

[olvyko]

Today u can only bail! and ensure! error message (&str).
I suggest adding the ability to return structs and enums that implement Fail trait.

Today:

bail!("error message");
ensure!(false, "error message");

Could be:

bail!(ErrorKind::SomeError);
ensure!(false, ErrorKind::SomeError);