Also, add a shared spec that ensures each matcher uses it.
…e_* or have_*
Expose `RSpec::Matchers::EnglishPhrasing` to make it easier to write nice failure messages and descriptions in custom matchers. Pretty remains private, and is still mixed into BaseMatcher and DSL::Matcher. EnglishPhrasing, by comparison, is not mixed into any classes, and its methods are now static.
Applies the same for `be_false`. Still fails as expected, but adds an additional message to suggest an alternative if still using the deprecated `be_true`/`be_false`. #741