Changy

- Fix: do not fail on initialization if `./changes` directory already exists.

- [gh-9](https://github.com/Tiendil/changy/issues/9) Reduced dependency versions restrictions to simplify integration in projects.

- Version files no longer contain a header. Instead, it is generated by Changy.

- Added checking for duplicated versions.
- Added custom exceptions for errors.
- Added meaningful error messages.
- Improved README.md.
- Better message for release commit.

- Added Changy steps to prepare-release.sh

Initial implementation.