Mkdocs-video

The HTML parsing mechanism has been rewritten using the `lxml.html` library.
Now the configuration is more granular due to the possibility of additional use of the [Attribute Lists](https://python-markdown.github.io/extensions/attr_list/) extension.

For more information, read [Configuration](https://github.com/soulless-viewer/mkdocs-video#configuration) section.

Support for the following `<video>` tag attributes has been added:

- loop
- muted
- controls

- added support for the `<video>` tag

* minor edits with CSS

* "relative paths error" for mkdocs >= 1.2 was fixed

Initial release