Added initial support for Ido language (similar to Esperanto).

It's a duplicate of CTRL_EMBEDDED.

this_ph_data, N_WAV_BUF, option.device, harm_sqrt_n,  max_hval, next_pause

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

There's two variables with the same name:
1) in struct PHONEME_DATA, used by *phdata, *phdata_next and *phdata_prev
2) an unnecessary one that's only being memset() twice but never used
   for anything

f_log is only used in compiledict.c.

See commit 65847bd251. Bool recursing is not used for
anything anymore. Fixes a (compiler warning.

It is memset and set once, but never checked or used for anything.

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().

global

    Wavegen2() only had one if-statement and then called
    Wavegen(). Wavegen() was never called directly.

Unsigned char *out_start is a global only used in speech.c.

SetSynth_Klatt() was using wvoice in two ways:
1) global wvoice was used directly
2) global wvoice was also passed in Wavegen_Klatt() as an argument "v"

Now the code only uses the function argument wvoice

Contributes to #68.

Contributes to #68.

Wavegen_Klatt2() only had one if-statement and then called
Wavegen_Klatt(). Wavegen_Klatt() was never called directly.

Update documentation to show already existing features and for
newly introduced `all` parameter.