Concurrent error handling utilities for Go.

errmux provides functions and data for working with concurrent error handling in a similar fashion to serial error handling. Unlike most error handling packages, errmux operates on channels of errors rather than errors themselves.

When a new Handler is created, errmux multiplexes all of its constituent error channel and passes the values to a Consumer for processing. All values on all error channels will be read - this is to prevent resource leaks due to blocking send operations upstream from a Handler. Errors will only be passed to a Consumer after reading if the following conditions apply:

1. Consumer has not previously reported that it is closed (c.Consume(err) == false)
2. Cancel has not been called on a Handler

If a Handler has been canceled, this does not guarantee further errors will not be read by the Handler. It does, however, guarantee errors will not be consumed by a Consumer.