Move from Voice Names to Voice Styles

[lornajane]

We use Voice Styles now, rather than voice names. Add support for styles, and update the docs to use this approach (bonus points if you can find Nicole in the new styles setup, she's my favourite!)

[thearavind]

Hi @lornajane Can I work on this issue

[lornajane]

You may, if you think you have enough information about the feature. The details for the changes to the NCCO are in the talk action docs: https://developer.nexmo.com/voice/voice-api/ncco-reference#talk and there's more information and examples about the styles in the text-to-speech guide. Thanks!