Shinywidgets

* Widgets now `fill` inside of a `fillable` container by default. For examples, see the [ipyleaflet](https://github.com/posit-dev/py-shinywidgets/blob/main/examples/ipyleaflet/app.py), [plotly](https://github.com/posit-dev/py-shinywidgets/blob/main/examples/plotly/app.py), or other [output](https://github.com/posit-dev/py-shinywidgets/blob/main/examples/outputs/app.py) examples. If this intelligent filling isn't desirable, either provide a `height` or `fillable=False` on `output_widget()`. (#115)
* `as_widget()` uses the new `altair.JupyterChart()` to coerce `altair.Chart()` into a `ipywidgets.widgets.Widget` instance. (113)

* `render_widget` now builds on `shiny`'s `render.transformer` infrastructure, and as a result, it works more seamlessly in `shiny.express` mode. (110)
* Closed 104: Officially support for Python 3.7.

* Actually export `as_widget()` (it was mistakenly not exported in 0.2.0).

* Closed 43: Fixed an issue where widgets would sometimes not load in a dynamic UI context. (91, 93)
* Closed 14: Added a `bokeh_dependency()` function to simplify use of bokeh widgets. (85)
* Closed 89: Exported `as_widget()`, which helps to coerce objects into ipywidgets, and is especially helpful for creating ipywidget objects before passing to `register_widget()` (this way, the ipywidget can then be updated in-place and/or used as a reactive value (`reactive_read()`)). (90)
* Closed 94: New `SHINYWIDGETS_CDN` and `SHINYWIDGETS_CDN_ONLY` environment variables were added to more easily specify the CDN provider. Also, the default provider has changed from <unpkg.com> to <cdn.jsdelivr.net/npm> (95)
* A warning is no longer issued (by default) when the path to a local widget extension is not found. This is because, if an internet connection is available, the widget assests are still loaded via CDN. To restore the previous behavior, set the `SHINYWIDGETS_EXTENSION_WARNING` environment variable to `"true"`. (95)
* Closed 86: Fixed an issue with `{ipyleaflet}` sometimes becoming unresponsive due to too many mouse move event messages being sent to the server. (98)

* Closed 79: make shinywidgets compatible with ipywidgets 8.0.5. (66)

* Stopped use of `_package_dir` function from `htmltools`.

* Miscellaneous typing fixes and updates.