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.

With the previous calculation, it was possible for the buffer to be
a byte or two too small to hold all of the data.

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

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

When notably the audio card is busy, we should report the issue to the
application, but still permit the application to retry submitting text
to synth, and eventually succeed to open it.

This change simply fixes the update of the out_samplerate variable to track
whether audio is open, and if not when text is submitted by the application,
try again to open it.

This is a partial fix for an audio regression. The other part of
the fix requires a change in pcaudiolib to reopen the audio device
on flush requests for affected audio drivers/devices.

This reverts commit f9ab812e00.

This fixes a regression introduced in commit
e341068d57.

This is needed for the case when espeak_Cancel is called before
calling espeak_Synth.

This reverts commit 26e453dd2f.

This is based on a patch by Samuel Thibault.

This is needed when espeak_Cancel is called before espeak_Synth,
like can be done in brltty.

This restores the behaviour removed in commit
ca831d236a.

When using eSpeak for audio and eSpeak in a server, using the async
speech requests, that code stopped the audio as soon as possible
from a cancel request. This allows servers like brltty to be more
responsive.

This reverts commit 1b5ea47ea4.

This patch is causing lockups when using this with servers like brltty.

This allows process_espeak_command to stop as soon as possible

Using emacspeak server with espeak-ng (still not published) found that audio was only being stoped after a command is processed (i.e. using pcaudiolib).
This fixes this issue.