Add version constant to library, bump version, and test

This pull request will add a `VERSION` constant to the library, making it easier to debug (e.g., *"before going any further, what is your `toopher.VERSION`?"*). 

I wrote a test to ensure that the version number exists in the library and is greater than or equal to this version, `1.0.6`, and wrote another test to ensure that the version number from the library matches the version number in the `setup.py` file used by PyPy/pip.