Fixes #1420 also Set max_digits to 32 for russian since it's safe to do now.

utf8_nbytes() is only used in dictionary.c. Others are moved to common.c

E.g. yue does not have many thousands separators, so the value may be very
large, possibly as much as maxint.

TranslateWord2 passes translator2 as tr to TranslateWord which may call
TranslateWord3, SpeakIndividualLetters, TranslateLetter, which was calling
SetTranslator2 again, thus freeing the very tr being used. Make that
latter use another translator.

These don't actually need to survive function exit.

So we know they are just tables, get protected from overflows, and get shared between processes

For the case when word is smaller than 4 characters, we should not look at
the 3rd or 4th character before checking the previous ones, otherwise
we'd at best read uninitialized data, at worse non-existing data.

This will make it easier to set a default voice other than
English. This is important for cases when a language will fall back to
the default voice.

Some references to L('e', 'n') still need to be changed.

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

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