1. Added the actual autotuner code. Minor modification - using 'sortBy'
on the populationList was causing a massive blow up in the compiler. The
error message is sufficiently complicated and abstruse to dissuade me
from finding the actual bug. Implemented brute force sorting of the
population keys by value (score).

2. Inserted the 'Tunable' class into OptiML.

3. Changed the IR node to take a Tunable parameter.

4. Currently the autotuner is less type-parameterized than the original
one. Once this is working smoothly, will add other types.