Upgrade to cmd2

[griffin28]

The latest documentation for cmd2 can be read online here: https://cmd2.readthedocs.io/
Main features:
Searchable command history (history command and +r)
Text file scripting of your application with load (@) and _relative_load (@@)
Python scripting of your application with pyscript
Run shell commands with !
Pipe command output to shell commands with |
Redirect command output to file with >, >>; input from file with <
Bare >, >> with no filename send output to paste buffer (clipboard)
py enters interactive Python console (opt-in ipy for IPython console)
Multi-line commands
Special-character command shortcuts (beyond cmd’s ? and !)
Settable environment parameters
Parsing commands with arguments using argparse, including support for sub-commands
Unicode character support (Python 3 only)
Good tab-completion of commands, sub-commands, file system paths, and shell commands
Python 2.7 and 3.4+ support
Linux, macOS and Windows support
Trivial to provide built-in help for all commands
Built-in regression testing framework for your applications (transcript-based testing)
Transcripts for use with built-in regression can be automatically generated from history -t
Usable without modification anywhere cmd is used; simply import cmd2.Cmd in place of cmd.Cmd.