Added a virtual environment for the project in the /venv directory.

Assuming you have python installed (http://www.python.org/getit/) as well as pip (http://www.pip-installer.org/en/latest/installing.html).

Run inside the TripCost directory:
`$ virtualenv --no-site-packages --distribute venv`
`$ source venv/bin/activate`
`$ pip install -r requirements.txt`

More information: http://stackoverflow.com/a/12657803/410166