Support Custom Tag(s) Search For API Source

Right now the posts that are queried for the API backlog source are narrowed down to just the [php] tag. I would like to add the ability to have a user choose which tag(s) they want to search under for bad posts. This feature is dependent on Issue #15 being fixed, otherwise it's a guarantee the server will be banned constantly. Each tag of course will be cached separately from each other in their own cache file.

Here is how I see the process happening, feel free to make changes:

1. User chooses new tag(s)
2. The backlog queues the new tag(s) to be queried and cached
3. Once the tags have been queried and we now have results, display the results
   If multiple tags are chosen we display them as one result, but in chronological order.

Things to consider:

1. How will cache updating happen?
   • Do we update ALL tags that have been used in backlog?
   • The most popular tags based on popularity on SO?
   • The most popular tags based on people trying to use that tag in the backlog?
2. Backlog will need an updater service to handle the cache updating and queue
3. Cron will be run every two minutes as usual, but will be dependent on the updater service handling the cache updating as well as processing tag queue
4. Can we offload the API queries to client-side since it is just a JSON response that way it won't count against the server's request and prevent banning?

This is in no way happening anytime soon, but would like some insight on how it might be done best so can plan ahead. So, thoughts?

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Related reading: https://github.com/Crell/fig-standards/blob/Cache/proposed/cache.md