[GreatFET] greatfet host version

[Carl Wall]

Tried the following on greatfet host software

cwall at debian2:~$ greatfet --version
ERROR: Unsupported subcommand '--version'.
Check to ensure the package providing the subcommand is installed.

Just thinking as things progress knowing what version of greatfet host will be
needed to help with trouble shooting bug reports.

Having to do the following would may not be intuitive for most users.

cwall at debian2:~$ pip3 show greatfet
Name: GreatFET
Version: 2019.5.1.dev0
Summary: Python library for hardware hacking with the GreatFET
Home-page: https://greatscottgadgets.com/greatfet/
Author: Great Scott Gadgets
Author-email: "removed by carl before posting"
License: BSD
Location: /usr/local/lib/python3.7/dist-packages
Requires: pygreat, ipython, pyusb, future
Required-by: 

Guess it could be covered in a FAQ on submitting bug reports, or have greatfet
host print out the version when you enter greatfet without any subcommands and
it prints out the help file of subcommands.

Carl