This removes the GUI part of espeakedit, keeping the part that is
responsible for compiling the voice and intonation data. The
motivation for this is:

  1.  the voice and intonation data compilation will move into
      libespeak-ng after removing the wxWidgets logic and converting
      the code to C;

  2.  the espeakedit code is tightly coupled to the internals of
      libespeak-ng at a source code level, not a binary/API level,
      making the code harder to maintain;

  3.  a new GUI will be written in Qt that better supports creating
      and editing voices and languages.

This is part of the process of making compiledata.cpp independent
of espeakedit.

This is part of the process of making compiledata.cpp independent
of espeakedit.

This moves the libespeak source (*.cpp) files to src/libespeak-ng
and renames the C files (libespeak, espeak, speak) so they have
a .c file extension.

The libespeak files are supposed to be C code, so use C linkage
for all the functions defined in that code when they are being
referenced in the C++ code (i.e. espeakedit).

StdAfx.h is only needed for Microsoft Visual Studio C++ projects
that specify the "use pre-compiled headers" setting.