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.
* add support to hashing module
* add dbhashsum to list the hashes
* add support to dropbox module
This means objects up and downloaded to/from Dropbox will have their
hashes checked.
Note after this change local objects are calculating MD5, SHA1 and
DBHASH which is excessive and needs to be fixed.
