Add auditor support for failing if certain assumptions exist

[atomb]

One use case for the auditor is to better understand the assumptions your code is making. Another is to ensure that you're not making assumptions of specific types (or never introducing more beyond a base set). For the latter case, it would be nice for the auditor to allow failing a build it detects assumptions of a certain type.

To ensure that no new assumptions are added, it may work to check the output of the auditor (maybe the Markdown version) into a repo and then have the CI check that the latest output always matches this initial version.