Also make Eigen format construction explicit

The notion of an instruction will probably come back
but with a different implementation.

This reduces compilation time by ~10x

Basic autodiff for +, -, *, /, exp, log, plus numeric testing support

* working unit test currently fails as expected

* unreferenced args unit test pass

* cleanup

* cleanup

that will be incrementally replaced

Multiply and Add numeric/autodiff unit tests pass

Documentation for all ops that have been defined so far. Includes numerous edits by @ECouzens.