Copier

- The `copier` command-line script now accepts "help" and "version" as commands.

- Task runner 🎉.
- Use `_exclude`, `_include`, and `_tasks` keys in `copier.yml` as the default values
for the `.copy()` arguments `exclude`, `include`, and `tasks`.

- Rebranded from `Voodoo` to `Copier`!
- Dropped support for Python 2.x, the minimal version is now Python 3.5.
- Cleanup and 100% test coverage.
- The recommended configuration file is now `copier.yaml`, but a `copier.json` can be
used as well. The old `voodoo.json` is also supported _for now_ but is deprecated
and will be removed in version 2.2.
- Python package format updated to the latest standard (no `setup.py` 😵).
- Renamed the `render_skeleton()` function to `copy()`. The function signature remains
almost the same, the only changes are:
- `filter_this` parameter is now called `exclude`.
- `ignore_this` parameter is now called just `ignore`.
- Dropped the idea of storing the templates in a hidden `$HOME` folder.