Added Example Project

Added an example project to more concretely demonstrate some of the affordances of this library. Updated the README to explain this example project, and also corrected an error in my description of how to produce a valid FormRequest using the REQUESTS_TO_ADD field in a local config file. Finally, cleaned up some ugly code in middleware.py, and made a small change in utils.py which will hopefully resolve the bug whereby it was impossible to update spiders with custom arguments that were edited within the spider's init function.