This reverts commit d08b8e43ca.

This commit causes gcc-4.8 to output a different SHA1 hash on the
language-phonemes test for `af` (the first language tested). It
does not break on clang or on gcc-7 so may be a compiler bug,
however the Travis CI build server is using it on Ubuntu Trusty
(14.04 LTS) and so may other older OSes.

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