Before this change FixRangeOption was leaving `Range: bytes=21-`
alone, thus not fulfilling its contract of making Range requests
absolute.
As it happens this form isn't supported by Cloudflare R2.
After this change the request is normalised to `Range: bytes=21-25`.
See: #5642
Nothing is added or removed and no package is renamed by this change.
Just rearrange definitions between source files in the fs directory.
New source files:
- types.go Filesystem types and interfaces
- features.go Features and optional interfaces
- registry.go Filesystem registry and backend options
- newfs.go NewFs and its helpers
- configmap.go Getters and Setters for ConfigMap
- pacer.go Pacer with logging and calculator
The final fs.go contains what is left.
Also rename options.go to open_options.go
to dissociate from registry options.
