`wym.exec` manipulation tests

Bold, Italic, Superscript and Subscript are the four commands that end up raw in the browser's `document.execCommand` interface.

We use `wym.exec` for other "commands" (for no obvious reason), which are picked up in `wym.exec`, their respective methods are called and they don't end up in `wym._exec` which later sends to `document.execCommand`.

So these tests are the four that actually end up in `document.execCommand`.