External python modules

This Pull Request extends the existing Python bindings to allow integration of 3rd party C++ libraries that depend on OpenCV.

The commits include a sample module that acts as a test for the changes. A more complete example of how this functionality works, can be found at https://github.com/derfred/asmlib-opencv. That repository contains a fork of the asmlib library found at https://code.google.com/p/asmlib-opencv/. In particular the file src/demo/demo.py demonstrates a port of the C++ based demo to Python.

The documentation is not yet done, but I will complete it should the PR be accepted.