Tweaks to improve Python versioning handling:
  - Change the shebang to use env to find python3.
  - Declare the MIN_MAJOR and MIN_MINOR of Python that is required.
  - Minimum Version Check function that lets the user know what the version requirement is if they do not meet them.
Merge pull request #2 from dfinlay/feature/py-version

Tweaks to improve Python versioning handling: