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.
Before this change calling core/command gave the error
error: response object is required expecting *http.ResponseWriter value for key "_response" (was *http.response)
This was because the http.ResponseWriter is an interface not an object.
Removing the `*` fixes the problem.
This also indicates that this bit of code wasn't properly tested.
If the parameter being passed is an object then it can be passed as a
JSON string rather than using the `--json` flag which simplifies the
command line.
rclone rc operations/list fs=/tmp remote=test opt='{"showHash": true}'
Rather than
rclone rc operations/list --json '{"fs": "/tmp", "remote": "test", "opt": {"showHash": true}}'
This adds expire and unlink fields to the PublicLink interface.
This fixes up the affected backends and removes unlink parameters
where they are present.
