Adding ability to use Resque for async processing
Got async updating of product prices working! Have some basic rate limiting built in, but I need to check Amazon's api docs to comply with their limits in the future.
Repurpose class to update all product attributes.

Class needs to be repurposed to update the whole product, including the
price. The Amazon API has a limit of one request per second, so the code
must be changed to only use the API through the scheduled async process
to accommodate that. Amazon's terms also specify that you have to refresh
product information *at least* every 24 hours, and this will allow for
that as well. I'll figure out how to make this scale for large numbers of
products later.
Change product fetching to be completely async.

Async process will now check the oldest product for updates every 5 seconds
but only save a new price instance if it has changed. Newly added products
only have an amazonid saved initially, then wait their "turn" to  populate
all of the actual product and price information.