This way the outputs are available for further downstream processing, e.g. with
grep. For TTS/bin/synthesize.py, if --pipe_out is set, log to stderr because
then only the output audio stream should be on stdout, e.g. to pipe it to aplay.
* Fix the bug in split_dataset
* Make eval_split_size configurable
* Change test_loader to use load_tts_samples function
* Change eval_split_portion to eval_split_size and permits to set the absolute number of samples in eval
* Fix samplers unit test
* Add data unit test on GitHub workflow