Add Festival TTS support

[jmontane]

Description

This PR adds Festival TTS engine suport #2640

How to test

Just install festival tts engine and voices (Catalan is a good example). And set mycroft settings:

{
    "module": "festival",
    "festival": {
      "lang": "catalan",
      "encoding": "ISO-8859-15//TRANSLIT"
    }
}

Contributor license agreement signed?

Yes, I do.

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[krisgesling]

Sorry, couple more things I just noticed while testing it out.

It would also be great if you can squash the commits into a single "Add Festival TTS engine". This helps to keep the commit history of mycroft-core cleaner, making it much easier to know what each commit is related to.

If you're not familiar with git it sounds scary but, here's a nice overview of how to do it. If you run into any trouble let us know.
https://stackabuse.com/git-squash-multiple-commits-in-to-one-commit/

[krisgesling]

It would be good to set 'utf8' as the default here so that by default we don't convert the text:

encoding = self.config.get('encoding', 'utf8')

Wondering if we also need a TTS specific lang config?

Looking at Festival it seems that they use the full names of languages eg "English" so self.lang will likely never be accurate. Could still provide it as a default:

lang = self.config.get('lang', self.lang)

So a users config might then look like:

{
  "tts": {
    "module": "festival",
    "festival": {
      "lang": "italian"
    }
  }
}

[krisgesling]

shell=True has some security considerations so ideally we can avoid using it. Unfortunately you can't use a simple pipe character without it.

One option would be to split each command into it's own call and pipe using subprocesses built in method. Eg:

        text = subprocess.Popen(('echo', sentence), stdout=subprocess.PIPE)

        if encoding != 'utf8':
            convert_cmd = ('iconv', '-f', 'utf8', '-t', encoding)
            converted_text = subprocess.Popen(convert_cmd, 
                                              stdin=text.stdout,
                                              stdout=subprocess.PIPE)
            text.wait()
            text = converted_text

        tts_cmd = ('festival', '--tts', '--language', lang)
        self.begin_audio()
        subprocess.call(tts_cmd, stdin=text.stdout)
        text.wait()
        self.end_audio(listen)

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[jmontane]

Hi, @krisgesling

Thanks for your help. I've tried my poor skills with git. I hope It's good enough now.

Regards

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[krisgesling]

This looks perfect, nice work!