Add new configuration to merge cache hits

- Specifically intended to get around analytics requests with
different URLs each time, sometimes even just slightly different
hostnames!
You are understanding me correctly, but I think it's more realistic to expect Request 3 use a different cached file than the other two because the data you're requesting is different.  Since you're the only user of this feature, I'll let it go as-is, but please update the README to mention that the request body is ignored for POSTs.