Prevents a segfault.

See issue #8, https://github.com/espeak-ng/espeak-ng/issues/8

There might still be some ints that could be changed to boolean.

Possible regressions in fifo.c:
int fifo_is_busy() and int fifo_is_command_enabled() used to return an int. Now they return a boolean. This might cause problems on systems where stdbool true/false is something else than 1/0.

Patch by https://github.com/ChliHug.

Moved include/espeak/speak_lib.h to include/espeak-ng/speak_lib.h and
created a symlink from the original location.

Added support for line-by-line input reading from unix FIFOs.

This makes the espeak-ng.c and speak-ng.c source code easier to
read and maintain. It also addresses bugs in command-line argument
parsing with the espeak implementation, for example it treats
`--compile-phonemes` as `--compile` due to an argument matching bug.

This reverts commits 0cc0300328 to
38d15f8f90.

The 0cc03003 commit breaks MBROLA voice support. As such, there
may be other breakages in those commits.

This commit has been reported to cause distortions in phoneme
pitches and speeds.

Also use size_t instead of int in some places
where it make sense