Propose adding new rule prefer-equal

[heath-freenome]

This article puts forth a very strong argument to using toEqual() over toBe(). So this new rule would be triggered if code is using toBe() instead of toEqual() for comparing things like strings or plain objects. If the prefer-strict-boolean-matchers is enabled, it would NOT complain when toBe() is used with true or false inside of it, otherwise it could.