Add Text to Speech extension!

[ericrosenbaum]

This enables the Text to Speech extension, which uses a server-side speech synthesis system:

• Use the speak block to say words and phrases up to 128 chars (including gibberish, or even your favorite song lyrics).
• Set the voice to "alto" (female voice), "tenor" (male voice), "squeak" (female voice pitched up), "giant" (male voice pitched down) or "kitten" (every word replaced with "meow" in a pitched up female voice).
• The voice setting is per-sprite, not reset by green flag/stop, and not saved.
• Set the language to one of several currently supported. Input text is not translated (but, as a side effect, you can get "foreign accents" this way. For example, with the French voice set, English language text will be spoken in a French accent). At the time the extension is loaded, it will set its language to the editor language, if it is supported by the extension.
• The language setting is global, not reset by green flag/stop, and it is saved and loaded with the project.

Yay!