0.9.7

1. Bug fixes;
2. Added dvc install for installing git post-checkout hook;
3. Support dvc checkout for a single file;
4. Support for reflink/hardlink/symlink/copy types of cache links;
5. Support for configurable and shareable cache dirs;
6. Stages without dependencies are now ran by dvc repro;
7. Dvc now checks for updates once a week and prints a warning if newer version is available;