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

Added detection of ==SUPPRESS== in subcommand group names to avoid printing it in the help hint.
Added some examples to tab_autocompletion to demonstrate how to tie in to cmd2 path_complete

Added support for tab completing application commands in ipython shell
Updated unit tests scripts to set cmd_echo to True to validate command output.

Removed all legacy pystate objects.
Changed default behavior to clear _last_result before each command
Added utility for creating named tuples with default values
Added tests to exercise new changes.