Soupsieve

- **FIX**: Fix pattern compile issues on Python < 2.7.4.
- **FIX**: Don't use `\d` in Unicode `Re` patterns as they will contain characters outside the range of `[0-9]`.

- **FIX**: Fix warning about not importing `Mapping` from `collections.abc`.

- **NEW**: Add `closest` method to the API that matches closest ancestor.
- **FIX**: Add missing `select_one` reference to module's `__all__`.

- **NEW**: Add `select_one` method like Beautiful Soup has.
- **NEW**: Add `:dir()` selector (HTML only).
- **FIX**: Fix handling issues of HTML fragments (elements without a `BeautifulSoup` object as a parent).
- **FIX**: Fix internal `nth` range check.

- **NEW**: Throw `NotImplementedError` for at-rules: `page`, etc.
- **NEW**: Match nothing for `:host`, `:host()`, and `:host-context()`.
- **NEW**: Add support for `:read-write` and `:read-only`.
- **NEW**: Selector patterns can be annotated with CSS comments.
- **FIX**: `\r`, `\n`, and `\f` cannot be escaped with `\` in CSS. You must use Unicode escapes.

- **FIX**: Fix issue with undefined namespaces.