z3 bindings

[mmcloughlin]

In support of #96 we need to be able to use the z3 library from ec3 via cgo.

[mmcloughlin]

Existing z3 bindings in Go:

• https://github.com/aclements/go-z3
• https://github.com/mitchellh/go-z3
• https://github.com/benbjohnson/glee/tree/master/z3
• https://github.com/skorobogatov/z3
• https://github.com/akreuzer/z3go/

Useful C API examples: https://github.com/Z3Prover/z3/blob/71d68b8fe082b5efb8cf9990e7275b3b97acbb62/examples/c/test_capi.c

[mmcloughlin]

The version of z3 provided by Ubuntu is too old, and there doesn't seem to be a custom apt repository with newer versions. Building a docker container for the build/development environment might be easier.

• Building and pushing to Docker Hub from CircleCI https://circleci.com/blog/using-circleci-workflows-to-replicate-docker-hub-automated-builds
• Using Docker Cache from CI Builds https://testdriven.io/blog/faster-ci-builds-with-docker-cache/

[mmcloughlin]

CI pipeline appears to be working on the custom image:

https://circleci.com/workflow-run/25bc1478-719c-4ac5-a9b8-cb0e6baf0df4