TO DO:
 - new implementation of debug messages:
   debug messages should be printed to .cdw.log file

 - full support for xorriso

 - remove unnecessary stuff from cdw_config_t, move it to cdw_task_t;
   create "cdw_task_t permanent_task" that stores parts of configuration;

 - corretcly handle situation when verifying a disc and an image file,
   and the image is larger than track on disc - cdio may throw an
   error while reading end of track, and cdw will interpret this as
   disc access error;


DONE:

 - add "-root" option in mkisofs options

 - move .cdw.log, .cdw.conf and .cdw.colors to ~/.cdw/

 - add support for ~/.mkisofsrc (but only reading the file)