Change error message when no files and no options provided to suggest --help option

[delphidabbler]

At present when CompFileDate is run with no parameters

Error: Exactly two file names must be specified

This isn't very helpful. It would be better if the program output either the complete or abbreviated help screen, such as

CompFileDate by DelphiDabbler (www.delphidabbler.com)
-----------------------------------------------------
Usage: CompFileDate filename1 filename2 [options]
  or   CompFileDate -h | -? | --help
  or   CompFileDate -V | --version

For further help use CompFileDate --help

[delphidabbler]

Implementation ideas:

1. Add new TParams.ShortHelp Boolean property.
2. Change TParams.Parse at lines 140/141 to set ShortHelp property to True if both file names are empty instead of raising exception.
3. In TMain.Execute about lines 218/219 to check if TParams.ShortHelp is True and call a new TMain.ShowShortHelp method to display required message.
4. Implement TMain.ShowShortHelp to display sUsage followed by new resource string for rest of the message, i.e.: 'For further help use CompFileDate --help'
5. Remove error code & message previously used when no file name provided, i.e.: cAppErrFileNamesSame and sAppErrFileNamesSame.