Enhancement - #307 show command

- introduced new show command to display configuration settings
- config command is used to just set config values
- modified documentation
- modified some unit tests calling 'task config' to 'task show'

src/tests/config.obsolete.t

@@ -40,7 +40,7 @@ if (open my $fh, '>', 'obsolete.rc')
 }
 
 # Test the add command.
-my $output = qx{../task rc:obsolete.rc config};
+my $output = qx{../task rc:obsolete.rc show};
 
 like ($output, qr/Your .taskrc file contains these unrecognized variables:\n/,
                'unsupported configuration variable');