Continue working on "template" tests, and add to CI

[robdockins]

PR #89 added a new testing paradigm to the What4 test suite. It generates syntactic templates and uses solvers as a computational oracle to test concrete evaluation of floating-point expressions.

We should extend this idea to other theories, and find some principled way to have these tests run as periodic CI jobs. They are probably too expensive to run on every commit/PR, especially if we extend the test to templates of depth more than 1.