Web updates

Web IDL dd6cccbdec18

Editorial: simplify the example on default toJSON() (#980) This example was adapted from a previous one in, but things are much simpler now and the example makes it seem more complicated than it really is. Make the points inheritance and mixins separately. This also fixes the order of attributes on the returned JSON object, which was wrong the original example. The attributes of the base interface should be included first. Reverse the inheritance order in the example to make this clearer, matching `interface B : A` in two other examples. Fixes #979.

Philip J├Ągenstedt