1. Use 'extras_require' in setup.py for backward compatibility;
0.16.4
1. Fix `dvc` help output; 2. Add more verbose messages for run/add/checkout; 3. Fix LD_LIBRARY_PATH issue with binary dvc packages; 4. Fix install_requires in setup.py;
0.16.3
1. Fix dvc --version that on some versions of python prints to stderr and on some stdout; 2. Fix install requirements;
0.16.0
1. Added `--dry` and `-i|--iterative` for `dvc repro`; 2. Added confirmation prompt for overwriting dvc files with `dvc run`; 3. Fixed README formatting; 4. Fixed `dvc` and `dvc -h` formatting; 5. Improved test coverage;