Add cmd2 to Command-line Application Development section

Created by: tleonhardt

What is this Python project?

cmd2 library for interactive command-line application development

• The goal of this project is to make it quick and easy for developers to create feature-rich interactive shell applications

What's the difference between this Python project and similar ones?

• Applications created are full-featured shells in their own right with ability to call shell commands, redirect command output, pipe command output to shell commands, etc.
• Superior tab-completion capabilities, especially when using included argparse decorators
• Both Python and ASCII text application scripting is built-in
• Ability to run non-interactively for automation purposes --

Anyone who agrees with this pull request could vote for it by adding a 👍 to it, and usually, the maintainer will merge it when votes reach 20.