Use os.makedirs to create full path to cache directory

Fixes issue #24 (closed) by using os.makedirs which creates all intermediate directories, whereas os.mkdir creates only the lowest level directory and assumes all other directories exist.

Replace the 'if not exists then create' logic with the exist_ok flag, that achieves the same outcome.

Signed-off-by: Anthony Kremor satnogs@anthonykremor.com