Made pruning of zeros and empty lists configurable.

Addresses issue #17, users can now specify whether zeros and lists should be pruned by setting the optional parameters pruneZeros and pruneLists. 
Take a look at: https://github.com/mewwts/addict/pull/22

Seems like there are two places we are choosing to check for pruneLists, once up at 102 and once again here. I took a slightly different approach of handling each of the "types" of item removals in their own section.

More than one way to skin a cat i guess :)