Pickled state variables

[ZJONSSON]

Request: filter.load(json) and filter.save() - allowing a pre-built filter (including dimensions / groups etc) to be loaded from JSON representation.

As state variables are not explicitly separated from local variables in the code, I find it hard to judge whether the this be a herculean task or whether the sheer size of the data would negate the benefits of pre-building (e.g. nightly node builds)

[RandomEtc]

As discussed in #151 an active fork is being developed in a new Crossfilter Organization. Please take further discussion there (if you haven't already) where it should be warmly welcomed by the new maintainers. Cheers!