Datafiles

- Fixed a `TypeError` when converting non-builtin attributes.

- Fixed ORM methods for datafiles with relative path patterns.
- Added plugin for `mypy` support.
- Updated YAML format to indent lists.

- Added ORM method: `all()`
- Added ORM method: `get_or_none()`.
- Added ORM method: `get_or_create()`.
- Added ORM method: `filter`.

- Added an option to automatically resave files after loading.
- Added an option to automatically reload files after saving.
- Added a registration system for custom converter classes.
- Added initial support for file inference via `auto(filename)`.

- Initial release.