This introduces a method of making provider specific configuration
within a remote. This is useful particularly in s3.
This commit does the basic configuration in S3 for IBM COS.
From testing it appears that CEPH no longer works properly with v2
auth and neither does Dreamhost, so update the docs anc configuration
to recommend v4 auth.
In a typical rclone copy to a bucket/container based remote, before
this change we were doing a list, followed by a HEAD of the bucket to
check it existed before doing the copy. The fact the list succeeded
means the bucket exists so mark it OK at that point.
Issue #1421
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.
