API: Allow Creation of Groups and/or Relative Date Criteria in Conditions

Hi there,

It would be really great if we could create groups via the API.

That, or the ability to use relative date criteria, such as YESTERDAY, etc as defined here, but as conditions in GET objects/contact calls:

- http://api.ontraport.com/doc/#rule-parameter-table

It currently works with fulldate type fields like Birthday (fortuitously), but does not with Timestamp type fields.

Here's an example condition used against /1/Contacts:

[{ "field":{"field":"date"}, "op":">", "value":{"value":"YESTERDAY"} }]