DateTime::Format::ICal bug

[Matt Sisk]

DateTime::Format::ICal 0.08 is not passing the dog food test and 
successfully parsing its own results. For example:

  $DTFI = DateTime::Format::ICal;
  $r = $DTFI->parse_recurrence(recurrence => 'FREQ=DAILY');
  $str = ($DTFI->format_recurrence($r))[0];
  print "$str\n";
produces 'RRULE:FREQ=DAILY'

Yet if we continue with that result...

  $r = $DTFI->parse_recurrence(recurrence => $str);

We get an error:
  invalid freq () at ... DateTime/Event/ICal.pm line 557
At issue seems to be that the parser does not remove the 'RRULE:' part 
from the beginning of a rule before splitting on semicolons.

Also, while we're at it, when we return these values can we either 
return a scalar when there is only one result (or make use of wantarray)?

Thanks,
Matt