Make "frozen" (self-contained) app and executable program 
distributions for Mac, Windows, and Linux.

NOTE: the version of Python you use to run the build scripts
here is crucial--it's the version bundled with the app/exe.

build2.0 used PyInstaller for Windows+Linux, and py2app for macOS.

build3.0, adapted from the PPUS app, now uses PyInstaller for all 
three PC platforms.  It makes standalone exes for Windows+Lunux 
snd a onedir folder for macOS.

It's anticiates that 3.1 will do the same for PCs as 3.0, but also
use buildozer for Android (along with a Kivy GUI for all).