reorganising stats and preprocessing nodes.  About to modify nodes so
they chain one to another rather than using pipeline.
making good progress in removing Pipeline for a more elegant design.
Still some work to do.  The disaggregation!
elecmeter.power_series() now accepts preprocessing nodes
Sped up datastore.load() by more than 100x
(previously it took about 11 seconds to load REDD
building1/elec/meter1.  Now it takes 0.073 seconds!)
finished converting processing nodes and results.  Now to get tests to
work again!
Tests all pass again!