Add support for Mimic

[Mimic](https://mycroft.ai/documentation/mimic/) is a compact speech synthesis engine developed as part of the Mycroft project, based on Flite, and largely compatible with it from the command line interface.

[An issue](https://github.com/MycroftAI/mimic/issues/91) already exist at Mycroft to add speech-dispatcher support for Mimic, but it doesn't seem to have been worked on. I thought it would be at least beneficial to raise it here for mutual awareness.