project revamped to provide new question every render

I was asked by someone to see if this project could be made to provide dynamic questions.  After I was done, I figured I would make the work clearer, add more tests and send you a pull request.  I did remove the sample project in favor of a single testing app, but I'm hoping you'll agree that less files/code cruft is easier to maintain.  Some of the tests do require the `mock` library, which I've added to a requirements/test.txt file.  If using virtualenv, just do:

```
pip install -r requirements/test.txt
python runtests.py
```

I also updated things to move support to python 2.6 - python 3.3 and Django 1.4+  The project is now testable with travis-ci.org, as I've included a travis-ci.yml file and turned on the hook for my account there.  You can see the test results against the different versions here: https://travis-ci.org/nkryptic/django-simple-math-captcha/builds/5051593

I hope you're still looking to maintain the project and that you can use these changes.  Let me know if you want anything adjusted further.