Dvc

1) Fix the message for dvc file formatting error;
2) Support `-f|--file` for `dvc add`;
3) Fix bug in ssh remote driver on windows;

1) Fix stage checksum calculation when `wdir` is default;

1) Multiple test improvements;
2) Fix a bug in `dvc repro`, when callback stages were not reproduced and instead a build cache was used;
3) `dvc status` with `--remote` now implies `--cloud`;
4) Raise exception when output/dependency doesn't exist. Previously this was handled properly only for local outputs/dependencies;
5) Use temporary file as an intermediary step when uploading to ssh remote to prevent cache corruption;
6) Use cache directory mtime/inode/size to do cache validation faster;
7) Support `dvc run --wdir` as a way to run dvc file command from a directory that doesn't match dvc file location;
8) Gracefully handle a case when a progress bar is interrupted with a prompt;
9) Support `dvc add` for symlinks that point to a location within or outside the current project;
10) Multiple code refactorings;

1) Use sftp for push/pull/status instead of full ssh;
2) Fix types in `dvc metrics`;
3) Fix `dvc move` bug with improper stage file resolving;
4) Fix a bug in external outputs caching, where we didn't check if cache already exists;

1) Fix bug in updating state db for cache and link during `dvc add`;

1) Add md5 entries for cache and link to state db during `dvc add` so that sequential commands don't have to recompute checksums for it;
2) Improve `dvc status` output;
3) Introduce `dvc commit` command along with `--no-commit` flags for `run/add/repro`;