Main changes:
* Change the listing order of files/directories so that the local and remote
snapshots can be compared on-the-fly.
* Introduce a new struct called EntryList that maintains a list of
files/directories, which are kept in memory when the number is lower, and
serialized into a file when there are too many.
* EntryList can also be turned into an on-disk incomplete snapshot quickly,
to support fast-resume on next run.
* ChunkOperator can now download and upload chunks, thus replacing original
ChunkDownloader and ChunkUploader. The new ChunkDownloader is only used
to prefetch chunks during the restore operation.
This is to avoid the read-after-rename consistency issue where the effect
of renaming may not be observed by the subsequent attempt to download the
just renamed chunk.
When connecting to Google Drive with a service account key, only files in the
service account's own hidden drive space are listable. This change finds
the given storage path among shared folders first so that folders from the user
space can be made accessible via service account.
When restoring a file that doesn't exit locally, if the file is large (>100M)
Duplicacy will create an empty sparse file. But this newly created file will
be mistaken for a local copy and hence the restore will fail with a message
suggesting the -overwrite option.
A new variable was added previosuly which caused a 64-bit variable to be not
aligned on a 8-byte boundary. Go still can't handle such variables on 32-bit
OS.
* CreateDirectory() looks up the directory in the cache first and don't create
it if found in cache
* ListFiles() puts subdirectories in the cache
* If CreateDirectory() encounters EOF, assume the directory already exists
* Restore/check should report an error instead of a success at the end if there
were any errors and -persist is specified
* Don't compute the file hash before passing the file to the chunk maker; this is
redundant as the chunk maker will produce the file hash
* Add a LOG_WERROR function to switch between LOG_WARN and LOG_ERROR dynamically
