This works around issue 915

Going through files in src/libespeak-ng/, include-what-you-use removed a
few unnecessary includes and included explanations on why a certain
header should be included. This makes tracking globals and dependencies easier.

Running the codebase through IWYU should be repeated after each major
code restIncludes to standard c library weren't checked to avoid
breaking builds with other platforms.

See https://github.com/include-what-you-use/include-what-you-use

It's only used in SpeakNextClause() and related to SelectPhonemeTable().

Another solution void be to keep SelectPhonemeTable() as a void function
and do a current_phoneme_table = voice->phoneme_tab_ix after the call to
SelectPhonemeTable().

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

This is from the old espeak RiscOS port that has been removed.

If/when the espeak-ng program is ported to RiscOS, this will be
done in a different, more maintainable way.

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