Contributes to #9.

So valgrind can potentially catch e.g. missing \0.

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

So they are protected from overflows, and shared between processes

When building espeak-ng in a directory that has a long path, 80 bytes to
store it is quite short.

See #950.

Soundicons are used for external audio with SSML <audio> tag and for
replacing punctuation names with sound files in LoadConfig().

Currently there's a bug wih soundicon slots: if both LoadConfig and
<audio> are used, the punctuation reserves all slots and no sound from
<audio> is played.

Instead of passing a temporary variable current_voice_id to SSML
processing logic and then copying the value to voice_change, pass
voice_change directly. GetVoiceAttributes() both sets voice_change and
retuns CLAUSE_TYPE_VOICE_CHANGE that is used by TranslateClause() for
error checking.

tests/ssml/language-switch.ssml covers the intended behavior of language
switching and will fail when either voice_change or CLAUSE_TYPE_VOICE_CHANGE
is not set correctly.

This adds a corresponding header file for mnemonics.c that was introduced in d5d93be.

It's unclear why c2 needs to be set after an entity reference.

ProcessSsmlTag()

Note the line in readclause.c:
if ((c2 == '/') || iswalpha(c2) || c2 == '!' || c2 == '?') {

It might be enough to pass everything to ProcessSsmlTag. What are the
cases that are skipped because of this?

This is a bit slower since we don't pass n_xml_buf as an argument but
rather get it with a call to wcslen. It is much cleaner though, since
the name ProcessSsmlTag() implies that all processing should be done
there.

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

This avoids 'unused parameter' errors in readclause.c.

The only entry point in the file is ProcessSsmlTags().

previous syntax was a quick fix when changing from globals to pointers.

use parameters instead of globals

move: attrcmp() and attrlookup()
new file ssml.c added to Makefile.am