Flottplot

New elements: `fp-controls`, `fp-calendar`

- Added `save` and `restore` actions and `url` attribute to `fp-state`.
- `fp-animation` now reports its state.
- `counter`-type item collections now accept input from the text box.
- Improved documentation.
- Internal improvements.

- Add video element
- Improve wrapping options for range and select
- Enable pass-through of attributes on elements
- Implement CLI and convert for Python package
- Improve documentation