Creating a 🐍📦 with an entry point

[dpshelio]

Help Charlene to have a command she can run from anywhere adding an entry point.

1. Choose who in your team is sharing now! (make sure you've pulled from your colleague's fork!)

2. Move the if __name__ == "__main__": block to its own file (e.g., command.py) and add it as entry point to setup.py

3. Add the dependencies of this library as requirements to setup.py.

4. Try to install it by running pip install -e . where the setup.py is.

5. Go to a different directory, run python -c "import sagital_average" and see whether the installation worked.

6. Share your solution as a pull request to Charlene's repository mentioning this issue (by including the text Addresses UCL-RITS/rse-classwork-2020#144 in the pull request description), remember to mention your team members too! (with @github_username)