Capture extra info using interface{ExtraInfo() map[string]interface{}}

[jsm]

Goal

Surface a way to be able to capture extra information

Related Issues

#134
#138
#146

How is this different?

• Instead of changing the API, which would be a considerable change, use an interface on error and provide a function to wrap the error with extra information.
• Allows setting extra information at the source, rather than having to manually do it wherever it's handled. It can be hard to pass the information needed up to the handler
• Works even wrapped with github.com/pkg/errors

Public API Changes

raven.WrapWithExtra(err error, extraInfo map[string]interface{}) error
raven.NewPacketWithExtra(message string, extra Extra, interfaces ...Interface) *Packet

type Extra map[string]interface{}

type ErrWithExtra interface {
	Error() string
	Cause() error
	ExtraInfo() Extra
}

[mattrobenolt]

This is clever. Could we get some tests? Otherwise, looks good. :)

[jheth]

Can this be closed now that #190 landed?