Migrate to using docusaurus, rather than docsify for documentation (#603)

* Add docusaurus documentation (to replace the docsify setup
* Remove older docs
* Specify documentation as the gh pages build action working directory

documentation/babel.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  presets: [require.resolve('@docusaurus/core/lib/babel/preset')],
+};