create ioperations to get multiple ids and urls in one call
first stab at caching multiple string and id funcs. also refactored them
added a get_all function to the redis cache backend. take advantage of the cache's get_all function if available (we may have cache types that do not support it)
small refactor
combine the nearly identical caching code for the multiple string and id functions into a multi-item decorator
some comments to clarify
moved the cache client out of the base minifier and into the cachedminifier
fixed an encoding issue for get_multiple_keys