The new IBM Watson TTS service now provides a unique url for your TTS
API resource. This adds a configuration option to override the default
url. As the url provided by IBM contains the api_path, we check for it
and if found remove it, as the RemoteTTS.__request method appends it
when making the call.
- Engines now specify if they support ssml rather than the configuration
- The text client strips out ssml tags
- Engines can modify tags via the `self.modify_tag` method
Kris Gesling
Åke Forslund
Luis Reinoso
Matthew D. Scholefield
Jarbas