[xml] New build process for Windows

[Igor Zlatkovic <igor stud fh-frankfurt de>]

Hello everyone,

the recent discussion about the command-line based build process for Windows
has been positive, if I am capable of any judgement. Thanks for the support.

I have commited the files required for this to both libxml and libxslt. The
files commited to libxml are:

  win32/configure.js      - Configuration script.
  win32/Makefile.msvc     - Makefile for MSVC/nmake.
  win32/libxml2.def.src   - Export definition source.

The files commited to libxslt are:

  win32/configure.js      - Configuration script.
  win32/Makefile.msvc     - Makefile for MSVC/nmake.
  win32/libxslt.def.src   - Export definition source (xslt).
  win32/libexslt.def.src  - Export definition source (exslt).

Of course, both have a readme file attached which explains the build
process.

Although libxslt and libexslt do not have conditional export table like
libxml, I have still supplied export definition sources, which are being
preprocessed to the actual export definition. This I have done for the need
of such conditional export table becoming necessary in the future.

Oh, and there is a present for Mark in there, the 'sodir' option to the
configure script :-).

The MSVC IDE facilities in win32/dsp are untouched by all this. Building
with the IDE is still possible.

Again, the win32 subdirectory of the libxml2 source tree contains a file
called Makefile.mingw, which was written by someone long ago to build
libxml2 using the GNU compiler, mingw edition. If someone using this
compiler is still out there and willing to brush up this makefile, we can
easily adapt the configuration script to support it.

Ciao
Igor