Post-unit-testing fixes.

 * change -n to mean "don't burn"
 * pass darbrrb args (e.g. -v, -n) through darrc
 * fix disc_title set number calculation
 * fix silly errors when running script not for testing
take happening out of disc_title: parameter is no longer needed
get rid of repeated "guards against" language
talk about what darbrrb actually is
warn user about writing their AES key in the script
re-wrap help message
add a couple of scripts to deal with expected sizes of par files.

PAR files are slightly larger than the redundancy data they contain, because of the checksums and headers involved. I want to get a rough idea of those sizes ahead of time, but being a new father have no attention span to work it out from the PAR source. So, empirical discovery it is.
make parpackets output lots of CSV data about a set of PAR files
allow for par redundancy files to be slightly larger than dar slice files