the index when using multiple base for sharding should be bound to the parse method instead of global

The state machine, denotate by `index`, was a module level variable, while parse method can be called multiple times. Not a big deal here because the routine is sync even though the api looks async. The side effect of this is that during the replacement of the base, sometimes we might not be using the first base for the first url in the file.

The main problem with this is that we might build the same application using shifter and we end up with different results, because shifter is truly async, which means that order it calls cssproc might be different, and the index fluctuations might affect the output.