when changing number of blocks, delete the persistent data from blocks that are no longer in use.
the "numbering" method of handling multiple blocks is not ideal - it should be named so that blocks can be
added/removed individually, regardless of where they fall numerically.
added debugging framework, including multiple debug levels (only 0-2 currently used)
bug fix (workaround) for PHP/SimplePie leaking memory
bug fix for google xml not giving correct results sortorder=ascenting
2500 events are no longer downloaded and pared down - it only requests
as many events as num_events. If you have multiple interleaved
calendars, this means num_events * N, where N is the number of
calendars, but it will take only the first num_events events.