szczanieckiej/redi_cache

* request
* check if $requestURI + etag in cache -> return
* download gtfs-rt trips + vehicles ->
  * check if in cache -> use
  * if headers have valid-to/from+for -> set ${feedID}/${type}ValidTo ${validTo} ; disappearing at $validity
  * else -> set  ${feedID}/${type}ValidTo $($(now)+30s) ; disappearing at $validity
  * save pb to ${feedID}/trips and ${feedID}/vehicles ; disappearing at $validity
  * or hash map from above
* download stop from API ->
  * check if in cache -> use
  * if headers have valid-to/from+for validity from headers
  * else -> validity $($(now)+30s)
  * save response ; disappearing at $validity
* download alerts
  * check if in cache -> use
  * if headers have valid-to/from+for -> set ${feedID}/${type}ValidTo ${validTo} ; disappearing at $validity
  * else -> set  ${feedID}/${type}ValidTo $($(now)+30s) ; disappearing at $validity
  * save pb to ${feedID}/trips and ${feedID}/vehicles ; disappearing at $validity
  * or hash map from above
* set ${requestURI} "${etag} ${validity} $(${payload}|base64)" ; disappearing at $validity