shinywidgets 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)