Editorial: Use WebIDL's new definition conventions for method/etc steps (#335)

* Per whatwg/webidl#730
  * The foo() method steps are: ...
  * The bar getter steps are: ...
  * The bar setter steps are: ...
* Pull some non-normative descriptive text for getters into notes.
* Somewhat more correct event handler attribute definitions.
* Wordsmithing around steps/properties in notes

Author: inexorabletash