md5sum, sha1sum are used by rclone.
cd, pwd improve the support for RemoteFiles mobile app.
These commands are all implemented inside SFTPGo so they work even
if the matching system commands are not available, for example on Windows
an user can now be disabled or expired.
If you are using an SQL database as dataprovider please remember to
execute the sql update script inside "sql" folder.
Fixes#57
