RS Cache: Store and retrieve variables from cache files

This class can be used to store and retrieve variables in cache files.

It provides a function to store the value of a variable of any type in a file of a given folder.

The file name is determined by a given unique identifier and an integer number that indicates the time when the cache file was created.

The class also provides a function to retrieve the cached variable value given its original unique identifier.

The cache life time limit is configurable. If it has already elapsed the life time limit when a cached variable is retrieved, the cache retrieval function returns false.

The class also provides a function to delete the cache files stored in the current cache folder.