Features:
* add local resources support: just set `local` parameter to `True`. See the [localfile2epub.py](https://github.com/dfface/xml2epub/tree/main/examples/localfile2epub) example for details.
* add local image cover support: for instance, just use `xml2epub.create_chapter_from_string("./local_file_example/03-06-OdnY0A.png", strict=False, local=True)`. See the [localfile2epub.py](https://github.com/dfface/xml2epub/tree/main/examples/localfile2epub) example for details.
Tips:
* If you want to add a cover image yourself, use the `create_chapter_from_string` method, then assign `html_string` to the image URL (e.g. `https://www.xxx.com/xxx.png`) and keep the `strict=False` parameter. Or assign `html_string` to the local image file path (e.g. `./xxx.png`) and keep the `local=True` and `strict=False` parameters.
* If the images and CSS files in your html are local resources, please set the `local` parameter to `True`, then the program will automatically copy the local resources instead of getting them from the Internet.