Update docs for Dropbox and Google Cloud Storage
local: calculate md5sum on Read or Update since we check it in Copy()
local: Make sure info is never nil
local: Implement Purger interface
drive: Flush directory cache on Purge
swift: Read metadata after Update or Put
s3: Read metadata after Update or Put
fs: Verify sizes are the same after transfer in Copy()
rclonetest: add --subdir flag for testing with a sub directory

Also add a test script for testing all the remotes
Version 1.02