There are small differences between diphone set of the voices, but they are not used from espeak-ng

There are small differences for diphone sets, but these are not used
from eSpeak NG.

A new 'hyw' language code has been registered for Western Armenian,
and the arevela and arevmda variant subtags have been deprecated.

This still accepts the hy-arevela and hy-arevmda language tags, but
uses the preferred names for the language files.

This is a Variant I created called male8, probably one of the smoothest sounding espeak male variants ever. It sounds very good with inflection at 100, which I don't know if you can only change in NVDA or other programs too.

These are some improvements to the german voices, both default and mbrola. It fixes some sounds of phonemes and also pronunciation of words. I also modified the mbrola phoneme and voice files to make them sound more natural. The stressLength setting is that it matches the way espeak deals with the lengths.

This reverts commit 0f55204522.

This breaks using voice files like mb-de5-en. It could also use
named values for the stress rules (e.g. 'first-syllable').

Keyword stressRule in voices.c handles setting langopts->stress_rule.

tr_languages.c still contains the setting for some languages that don't have a language file yet.

Contributes to:
Issue #218, https://github.com/espeak-ng/espeak-ng/issues/218

Contributes to:
Issue #218, https://github.com/espeak-ng/espeak-ng/issues/218

Changes:
language files have a new keyword letterVowel. It can be a latin alphabet from a-z or a hex value (used by bulgarian).
Errors in parsing the values are only reported, nothing is done about them.

About testing:
I haven't noticed any differences in the output audio with letterVowel set or unset in any tested language. The code seems to work and the correct bits seem to be set, but I don't know how to confirm from the final audio.

TODO:
1. Write better documentation in docs/voices.md
2. The code uses new_translator. Should it use translator instead?

Add ar1 mbrola support
Modify ar2 mbrola support

This is because the emoji are language specific.