Datetime queries do not have a flexible format

[mileswwatkins]

We should be able to flexibly search in datetime fields. The docs suggest that one could use everything from year alone to full datetime down to fractional seconds.

For example, this works:
http://api.opencivicdata.org/bills/?created_at=2015-04-09T00:24:06.485090
But this (and other variations on datetime) doesn't work:
http://api.opencivicdata.org/bills/?updated_at=2015

[mileswwatkins]

Same with votes; currently you have to search on full date string, even though the time component is null:

• Works: http://api.opencivicdata.org/votes/?start_date=2011-04-19%2000:00:00
• Doesn't work: http://api.opencivicdata.org/votes/?start_date=2011-04-19