CLI main menu update: usability improvements
CLI main menu update: usability improvements

There were some basic usability issues that needed to be addressed.
This commit makes the following changes to `bin/gftools`:

- Added a `-v/--version`, prints version number from `setup.py`.
- Added an ASCII graphic with built-in version number.
- Basic formatting work to conform to `pycodestyle`.
- Added a short list of basic command examples.

Resolves: #75

googlefonts/gftools,googlefonts/gftools