do not support a debug build for OpenSSL

This is not very useful as crashes are unlikely to happen in
dependent libraries.
avoid using print statement in the build script

This ensures that the output is flushed properly when redirected to
a file, and is a step towards achieving compatibility with Python 3.
implement a more generic approach for building dependent libraries

This will allow us to build more dependent libraries in the future.
use system libraries for zlib, libpng and libjpeg

This is implemented for Windows, Linux and the POSIX builds. For OS X,
we use the bundled versions of libpng and libjpeg as they may not be
available at runtime.
make the build script more compatible with Python 3