Announce zoom

[prushforth]

Per "2 The zoom level should be announced", we should make it so that the zoom level is always announced when it changes.

[prushforth]

• Update Web-Map-Custom-Element to audibly render zoom in output by default i.e. on by default
• Update MapML-Extension to reflect the fact that the option to audibly render zoom is on by default, provide option to turn it off. "Announce movement for screen readers" -> "Announce Zoom"
• Update Web-Map-Doc.
• Change the name of this experiment. We should add the pan/zoom control to that map, as well as a <map-caption>Paris, the City of Light</map-caption>