Extension to tiddlyweb select filters to use relative time statements.

Where a filter is:

select=modifier:>2011

one could expect either a tiddlywiki timestamp string, a fragment thereof, or some numbers that end with 'd', 's', 'm', 'h', 'y' (case insensitive) meaning Days, Seconds, Minutes, Hours, Years. We don't worry about months. If the trailing letter is there, we translate it into an absolute time in the past, relative to now.

It's important to note that the translation happens before the > or < is interpreted. So while

select=modified:>1d

at first glance reads as "select those entities with a modified more than one day ago" it is actually, if we say today is 20110302, "select those entities with a modified greater than 20110302" (i.e. those thing modified within the last day).