This is done to make clear ownership over accounting object and prepare
for removing global stats object.
Stats elapsed time calculation has been altered to account for actual
transfer time instead of stats creation time.
- 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.
Aleksandar Jankovic