errors package only provides reporting of log messages and recovery and report of panics. The package instead should provide APIs that can report Go errors.

I suggest to change the Report API to work against an error:

func (c *Client) Report(ctx context.Context, r *http.Request, err error)

Then, we can also remove the Reportf and users can use fmt.Errorf if they want to include more context to the error messages.

/cc @jba @zombiezen