Reload CC:T documentation index periodically

[SquidDev]

• Add a massively over-engineered caching system. If an item was requested within x seconds, we'll reuse it. Otherwise recompute it.

• Using this system, provide a mechanism for making cached HTTP requests. As well as the above TTL, we also use the ETag system to avoid receiving massive responses.

• We use the above to fetch the CC:T method index at most every 60 seconds.

  This does introduce a small latency, but doesn't appear to more than 0.2-0.5s on my terrible WiFi, so should be much faster when running on your server.

  We may wish to extend or shorten this delay later on - it means method changes should be picked up fairly quickly, though I realise they don't change /that/ often.

[Wendelstein7]

Over-engineered? Sure. Awesome? Obviously.

Merging! Thanks for the addition! ♥