- Change rclone/fs interfaces to accept context.Context
- Update interface implementations to use context.Context
- Change top level usage to propagate context to lover level functions
Context propagation is needed for stopping transfers and passing other
request-scoped values.
- make Close permanent and return errors afterwards
- use RangeSeek from the wrapped reader if present
- add a limit to chunk growth
- correct RangeSeek interface behavior
- add tests
