Pyghtml

- Added "with" statement support for container elements.
- Improved and expanded list methods.
- Added utility functions (see `README.md`).

- Added `py.typed` so `mypy` doesn't scream at you
- Added `property` to `<meta>`
- Added basic support for `<svg>` and `<use>`

None` is skipped when converting attributes into HTML-strings (including `None`s within lists and dictionary values).

- Added more list-like methods for containers (which work on heir `inner_html`)

- Initial release for `pip`.
- More or less stable architecture.