Don't print complete help text on argparse error

[kmvanbrunt]

ACArgumentParser overrides argparse.ArgumentParser's error() function. One of its behaviors is to print all of the help text when there is a parsing error. Help text can be pretty long and has the tendency to scroll the actual error message off the screen.

I suggest we use the normal behavior of only printing the error and usage statement when a parsing error occurs.

[tleonhardt]

@kmvanbrunt Your suggestion sounds like a good one.

[kmvanbrunt]

The error() function in ACArgumentParser prints its error in Fore.LIGHTRED_EX like perror() does. But this code was written before we added the colors setting in cmd2.

Should we make colors a setting that is shared across modules so ACArgumentParser and other modules in a cmd2 app can access it?

[tleonhardt]

It would perhaps be good to add the default error and warning colors to a common location such as constants.py.