Add function to parse common point set command options

[schuhschuh]

Common options for commands that write point sets to VTK files:

    if (OPTION("-ascii" ) || OPTION("-nobinary")) ascii = true;
    else if (OPTION("-binary") || OPTION("-noascii" )) ascii = false;
    else if (OPTION("-compress"))   compress = true;
    else if (OPTION("-nocompress")) compress = false;

Could be added to mirtkPointSetUtils.h as the boolean ascii and compress flags are passed on to WritePointSet or WritePolyData, respectively.

Corresponding help output code for copy-and-paste later:

  cout << "  -ascii/-binary   Write legacy VTK in ASCII or binary format. (default: binary)" << endl;
  cout << "  -[no]compress    Write XML VTK file with or without compression. (default: compress)" << endl;

[schuhschuh]

• HANDLE_POINTSETIO_OPTION macro to parse options.
• Add common function to print help of these options.