@jbenet @whyrusleeping @mappum

very helpful for tracking down errors. the stack traces are only
shown when debug mode is visible. They function best when caught at the
source.

I propose we use this errors package as a drop-in replacement for
fmt.Errorf and errors.New in all of our code, and use errors.Wrap for
external errors as they emerge from others' libraries.

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
Signed-off-by: Brian Tiger Chow <brian.holderchow@gmail.com>