Merging branches master and aleaverfay/vectorize_lj:
10% speed up for the etable evaluation.
I'm changing the way the etable calculates the "cubic splines"
that it uses to smoothly ramp the potential when it turns off.
The new code evaluates the same spline polynomials, but doesn't
use the cubic-spine formulation (which requires 8 additions, 13
multiplications and 1 division) but rather a cubic-polynomial
formulation (which requires 3 additions and 3 multiplications).
(The branch name is deceiving: the etable calculation is not
being vectorized)
Numeric changes result in 89 integration test trajectory changes.
However, the score-function-fingerprint benchmarks do not change.