These classes are subtly different, particularly in terms of their truthiness.

CmdResult
- attributes:  out, err, war
- truthy:  if err is falsy

CommandResult
- attributes:  stdout, stderr, data
- truthy:  if err is falsy AND data is not None

So CmdResult was oriented to provide essentially info, error, and warning messages to the user (typically as stirngs), whereas CommandResult is geared towards providing info and error messages to the user as strings in addition to data to the user in a command-specific format which is arbitrary other than it should never be None if the command succeeds.

Also:
- Converted global can_clip variable to an instance attribute of cmd2.Cmd class

Also:
- Added a few more type hints

Also:
- Refactored perror() to remove a rarely used optional argument which was unecessary