Build an initial demo for recommended voices

[HadrienGardeur]

In order to illustrate the effectiveness of documenting recommended voices, I've started building a demo.

In its current iteration this demo can:

• list all of the main languages covered by this project
• fetch the JSON configuration for that language
• fetch the list of voices available (using getVoices()) and filter this list based on the name and alt names of recommended voices

It's not currently my goal to cover everything mentioned in the best practice document for voice selection, but this is a decent starting point.

Things that I might cover in the future would include:

• hide languages with no voice available on the current system
• fallback to the full list of voices when there isn't a recommended voice available
• grouping up voices by region and displaying the user's preferred region on top

If I ever turn this repo into a real code repo as discussed in #9, then this demo will have to be a lot more extensive than it currently is.