* drop python 3.5 support
* dvc: remove fspath() use inside os.path calls
* dvc: replace dvc.compat.fspath with os.fspath
* tests: replace dvc.compat.fspath with os.fspath
* utils: relpath() should use fspath/str
* utils: os.readlink doesn't support path-like obj on Windows until 3.8
* remote: locally index list of checksums available on cloud remotes
* fix review issues
- use pytest fixtures
- use sha256 digest
- s/fd/fobj/
- check more specific IO errors
* remote: use .dir checksums to validate index
* command: add --drop-index option for push/pull/status
* tests: --drop-index unit tests
* remote: make index threadsafe
* remote: force re-index after gc
* only save/dump index once per command
* remote: add helper index functions update_all/replace_all
* remote: store index as sqlite3 database
* fix deepsource warnings
* rename --drop-index to --clear-index
* rename index.invalidate to index.clear
* functional tests for remote.index
* fix index not being updated on status -c
* remote: add index.intersection()
* remote: use index when making assumptions about remote .dir contents
* add missing func tests
* do not index standalone files
* cleanup index test fixture
* fix deepsource warnings
* update autocompletion scripts/cli help message for --clear-index
* tests: remove unused mocker
* push: only index successfully pushed dirs
- do not index files on partial push/upload
* remote: revert behavior to trust .dir files on remote
- skip unnecessary index check for dir contents if .dir file exists on
the remote
* fix missing RemoteIndexNoop functions
* separate index validation from status dir exists query
* bugfix: include indexed checksums for all cache_exists cases
* review fix: cleanup debug messages
* tests: fix DS warning
* remove --clear-index
* remove unused index functions
Peter Rowlands (변기호)
nik123