This makes the codebase more consistent. Including speech.h is not necessary anymore in some files. Includes have been removed.

synthesize.h now contains the definitions STRESS_IS_... that should be used with code related to syllable stress.

Note that isBreak and other defines were renumbered so that stress definitions could have values 0-6.

Possible TODOs:
1. Unify with terms used with phonemes, i.e. keywords like isDiminished in compiledata.c and stress_type in phsource/phonemes
2. Add functionality and documentation about STRESS_IS_PRIORITY and STRESS_IS_EMPHASIZED

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.

This fixes the clang warning:

    comparison of unsigned expression < 0 is always false
    [-Wtautological-compare]

Reported by Reef Turner <[email protected]>

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

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