Testing
-------

To run all unit tests, run:

make test

Design notes
------------

* For each variable, we compute and save all needed statistics on the variable
  in the initialization of that variable's object. These statistics can then be
  queried or printed later.

  This is more complex than just computing statistics as we need them (e.g., by
  the __str__ method). However, the current design allows the variable's data to
  be garbage collected after the computations are done, saving memory. In
  addition, this allows for the separation of computation from printing of
  results, which could lend itself better to parallelization of the computations
  (parallelize the computations, but serialize the prints at the end).