Fixed uninitialized memory in variable step size integrators
Fix small bug in unit related to mutable sequences.
Fix the mean() and std() methods on container Quantities when those containers
are NOT numpy arrays.
Add a set of unittests for the simtk.unit package. Implements most of what I
found in doctests.py (and quite a bit more, too)
chemistry.unit -> simtk.unit
Merge pull request #756 from peastman/variable

Fixed uninitialized memory in variable step size integrators
Optimization to CPU PME
Merge pull request #758 from peastman/fftw

Optimization to CPU PME
Merge pull request #750 from swails/fix_unit

Fix small bug in `simtk.unit` related to mutable sequences.
Fix typo.