This reduces the surface area of our `Kernel` monkeypatch and removes
the need to `include Kernel` in a bunch of modules.
While we're here, also move `Kernel#require?` to `Homebrew` and fully
scope the calls to it.
This was in the (soon to be archived) Homebrew/homebrew-bundle
repository's `README`. There's some good content here that doesn't
cleanly fit into the `brew` manpage so let's move it here.
While we're here, let's de-emphasize `whalebrew` as it's not
widely used and add commented-out deprecation warnings for its future
deprecation.
