Cleo exec modules are simply perl code.

They MUST:
     - include declaration of $cleo variable, containing version of
       module.
     - include declaration of subrutines:
       - ok
       - fail
       - post
       - pre
They MUST NOT:
     - include declaration of any packages

Example of module:

-----------------------------------
use vars($cleo);

$cleo=1.0;

sub ok( $ ){
    # called when task is finished successfully

    $_[0]->{id}; # this is task id
}

sub fail( $ ){
    # called when task is finished unsuccessfully
}

sub post( $ ){
    # called when task is finished
}

sub pre( $ ){
    # called when task is about to run
}
---------------------------------------

To all subroutines is passed one argument - reference to hash,
containing all task properties.

list of task properties can be taken from sceduler description
(README-sceduler-create)
