#2 Add expiration option to ad campaigns

[Greg Meiste]

This feature probably won't make the initial release of the module, so I'm submitting this RFE to be a reminder.

It would be nice to be able to set an expiration date on ad campaigns. This way, if an advertiser pays for 3 months of advertising, the ads are automatically pulled at the end of the three months. Without this, site admins will have to manually pull the ads, which could lead to free advertising if forgotten about.