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.
- 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.
* Implement about for:
* local, crypt, cache, drive, swift, hubic, onedrive, pcloud, dropbox
* Implement `--json` and `---full` flag for `rclone about`
* change About interface to return a Usage structure
* Remove operations.About as it is too thin an interface
* Implement Integration test
Relates to #1138 and #1564
