New features
* Added support for interacting with plots made with matplotlib, seaborn, and plotnine. (392)
* The `req()` function now returns its first argument (assuming none of its arguments are falsey). This lets you perform validation on expressions as you assign, return, or pass them, without needing to introduce a separate statement just to call `req()`.
* Added `Input.__contains__` method, so that (for example) one could write an expression like `if "x" in inputs`. (402)
Bug fixes
* The `width` parameters for `input_select` and `input_slider` now work properly. (Thanks, bartverweire!) (386)
* When `input_select` or `input_selectize` were not given an explicit `select` argument, they always chose the first item, which is correct when `multiple=False`, but not when `multiple=True`. Now when `multiple=True`, the first item is no longer automatically selected. (396)
Other changes
* Switched to new types from htmltools 0.1.5. (416)