fixes #170

fixes #30

fixes #379

…so it can be used to add browser support info in CSS IntelliSense.

…and capitalise GET / POST. Old get/post set is still needed for
formmethod on input and button.

…auto isn’t a valid value for draggable. true/false/auto isn’t needed
once that uses a boolean.

…auto isn’t valid when using on <bdo> element, so need to find how to
show that. It is valid for the global dir attribute.

* Add menuitem element and define valid values for menuitem type
attribute
* Add valid values for menu type attribute
* Add menu to valid button values
* Remove old command element

…as used by Web Components.

…no longer valid in HTML5.1 and WhatWG HTML