Fix laws

[hdgarrood]

This PR includes #23 plus the following changes:

• uses any and all in the laws, as @paf31 suggested
• adds a brief explanation of the less intuitive laws

I think this is now good to go, all the discussion points which were raised in #23 have been addressed.

[garyb]

Looks great to me!

[hdgarrood]

Fab. In that case the only outstanding question is whether this counts as a breaking, minor, or patch-level change. I would argue that this should be a patch-level change, as the current set of laws is actually incorrect for pretty much every instance, and I am fairly confident that this new set of laws matches people's assumptions and intuition about how this class should be used, i.e. I expect people will have been using this class as if it had these laws already.

[hdgarrood]

🎉