Also:
- Added optional err_color and war_color arguments to perror() for providing color escape codes
- Removed usage of deprecated colorize() method within the examples

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:
- Made self.locals_in_py = True for main.py and examples/python_scripting.py
    - This makes debugging easier in the embedded IPython shell provided by the opt-in ipy command

Added some shared definitions to cmd2/__init__.py -> maybe there's a better place for these?
Figured out how to trick bash into showing argument hints. It's a bit weird.
Updated all of the tests and examples to import cmd2 resources from their new location without the automatic imports in cmd2/__init__.py
For #369

Removed all dependency on six other than for six.moves.input

Also:
- Started removing code branches which were for Python 2 support