Incompatible with espeak-ng

[paper42]

Many distributions are moving from espeak to espeak-ng, but gespeaker is not compatible with it, because espeak-ng uses /usr/share/espeak-ng-data/ instead of /usr/share/espeak-data/ in engines/engine-mbrola.py and engines/engine-espeak.py

https://github.com/espeak-ng/espeak-ng#espeak-compatibility

The espeak-data data has been moved to espeak-ng-data to avoid conflicts with espeak. There have been various changes to the voice, dictionary and phoneme files that make them incompatible with espeak.

There might be other changes necessary.