Investigate replacing Structure101 with ArchUnit

[jzheaux]

Given that ArchUnit is open-source, it may be a better fit for capturing package tangles. We may be able to use it in the same way that Spring Framework does.

Note that we'd want to examine the tangles that Structure 101 captures and see how well ArchUnit does with the same.

[therepanic]

Hi, @jzheaux! Can I work on this issue? Can you assign me?