Log Message:
Update to 0.5.6:

0.5.6
-------------

Added --substitute which mimics Perl's s/old/new/(gi) substitution.
It can be used to replace substrings in output filenames.

Example:
  % cclive -S "s/old/new/i" URL
  % cclive -S "s/[/:-]/_/g" URL

Changed --regexp to accept Perl-like regular expressions, e.g.
  % cclive -r "/(\w+)/" URL
  % cclive -r "/(\w+)/g" URL
  % cclive -r "/([a-e])/gi" URL

Note that this breaks the backward compatibility.
  * --regexp now expects /pattern/(gi)
  * --find-all is no longer supported (use /g instead)

Added --background which is similar to what clive (2.1.x) once had.
The progress indication while in the background is very simplistic.
Note that --logfile and --logfile-interval options were also added
to support --background.