The cache option allows the user to select the underlying Spyce caching
implementation used. The format of the string for this option is
"type:info", where the type specifies the cache type, and the
optional info parameter is passed on to the cache implementation for
initialization. Spyce currently supports the following cache implementations:
memory: This is the default cache type, which uses an in-memory
dictionary to store the compiled Spyces. It takes no parameters.
file: The file-based cache type will serialize the compiled
Spyces and store them in a given directory. The info parameter should be the
directory location.