Support Google SSML

[rikhuijzer]

Google supports the Speech Synthesis Markup Language (SSML) which allows for more control over the audio.
For example, you can add pauses or emphasis to the audio:

<speak>
    This is an <say-as interpret-as="characters">SSML</say-as> example with a pause.
    <break time="3s"/>.
</speak>

But this needs to be sent correctly to the API:

"{
    'input':{
     'ssml':'<speak>The <say-as interpret-as=\"characters\">SSML</say-as>
          standard <break time=\"1s\"/>is defined by the
          <sub alias=\"World Wide Web Consortium\">W3C</sub>.</speak>'
    },
    'voice':{
      'languageCode':'en-us',
      'name':'en-US-Standard-B',
      'ssmlGender':'MALE'
    },
    'audioConfig':{
      'audioEncoding':'MP3'
    }
  }"