Extensions are now passed to the `JsPsych` constructor via an `extensions` option.
Along the way, the webgazer plugins and plugin-html-button-response have been modularized as well.
Co-authored-by: bjoluc <mail@bjoluc.de>
Co-authored-by: Becky Gilbert <beckyannegilbert@gmail.com>
* Convert jsPsych and plugins to ES6 modules
* Create packages for each plugin, the core library, and config files
* Setup rollup, jest, and babel configurations
* Update jsPsych to load plugin objects directly from the `type` field
* Update tests to use the ES6 modules