+0.6.6: Add in a couple of new template filters: total_seconds, and total_seconds_sort.
+ The latter zero-pads the value to 10 places, ideal for lexical sorting.
+ This correctly sorts timedeltas of up to around 10 years, if you need more
+ you can pass an argument to the filter.
0.6.5: Empty string values in database now are returned as None for the field value.
Note that you must have field.null=True to store a NULL in the db.
I'm still not 100% happy with this: postgres may choke on empty string values when doing INTERVAL comparisons.