Allows pip to install modules with the --user option on computers that use Homebrew.

Python installed with Homebrew has a bug. When a user tries to install a module using `pip install --user`, the installation will fail. A quick workaround is adding `--install-option="--prefix="` to the command options.

When Homebrew install Python (or any other program), it installs the program under /usr/local/Cellar, but places a symlink under /usr/local/bin (which is what is on your $PATH.)

Well, this code checks which version of Python is being used. If it see that the Python you are using is installed under ../../../Cellar/Python/...., it uses an additional option that will make it possible to install flask and ner.