refactor: expose public API

[ainghazal]

Expose config and tunnel as a public API.

This refactor tries to expose all the useful functions to instantiate an OpenVPN tunnel (paving the way to usage from probe-cli).

Checklist

• I have read the contribution guidelines
• Iff you changed code related to services, or inter-service communication, make sure you update the diagrams in ARCHITECTURE.md.
• Reference issue for this pull request:

[ainghazal]

Deferring review until we merge #68 (which is included in this branch right now).

[hellais]

This looks good to me.

From an inspection it looks like the only thing that's really changing are the import paths for model and tun, which are moved out of the internal package.

In light of this some code is also moved around a little bit, where the most noticeable difference is the tunnel.Start method which takes the code which used to live inside of main.

The only question I have is why the logger_test and tracer_test were removed? Is it because this new layout makes testing of those packages harder?

All in all, this looks good to merge for me!

[ainghazal]

The only question I have is why the logger_test and tracer_test were removed? Is it because this new layout makes testing of those packages harder?

it was a bit of a cleanup:

• logger_test was providing a test logger for other tests to use; this was moved to model.mocks.TestLogger
• similarly, tracer_test provided only a no-op implementation of model.HandshakeTracer; I decided that I can pass model.DummyTracer to all tests that need to receive a tracer.