Fixed some bugs and added new tests

New test_multi_03 can be used to test multiple variables at once. Based on new collect function that can be used to collect n variables from parsed Ziffers.

ziffers/__init__.py

@@ -1,6 +1,5 @@
 from .parser import *
 from .mapper import *
-from .classes import *
 from .common import *
 from .defaults import *
 from .scale import *