Historically, tools have been a subclass of reviewbot.tools.Tool. We

later added a second base class, reviewbot.tools.RepositoryTool, for

tools that needed a full repository checkout. The fact that that

capability was a base class, and not a mixin, made it hard to introduce

any new base classes, which an upcoming change will do.
To prepare for that, and to keep things organized, a new

reviewbot.tools.base module has been created, with provides

reviewbot.tools.base.tool.BaseTool and

reviewbot.tools.base.mixins.FullRepositoryToolMixin. These are aliased

into reviewbot.tools.base, for convenience.
No tools have been updated yet for this change. Some further work will

be done on the base classes first. Tool updates will come in a series of

changes after this has been completed.

Unit tests pass.
Ran the worker and verified it was able to scan tools and check

dependencies.