Superoptimization

This issue is for tracking progress on the super-optimization component. This component solves the challenge of generating a script that is likely to exhibit the highest possible performance for the available script, input data, and broader environment. The script that meets these requirements may well be the sequential script — in which case, `pash` needs to avoid delaying its execution at all costs. Keeping the fastest path fast will be challenging, because this component will incorporate some exploration of a configuration search space.

More discussion in the [docs/superopt](https://github.com/andromeda/pash/blob/master/docs/superopt.md) document.