As of Go 1.16, the same functionality is now provided by package io or package os, and those implementations should be preferred in new code.
This is possible now that we no longer support go1.12 and brings rclone into line with standard practices in the Go world. This also removes errors.New and errors.Errorf from lib/errors and prefers the stdlib errors package over lib/errors.
Fixes #118 Co-authored-by: Chris Nelson <stuff@cjnaz.com>
