`wrap_comments` doesn't reflow text.

Another one for wrap_comments:

/// this
/// is
/// an
/// unnecessarily
/// tall
/// comment.
fn foo() {}

The formatter doesn't format these comments

While this may be desirable in some cases, (e.g. TODOs), in light of #627, perhaps a better general solution is to add a markdown formatter and use it inside doc comments, since those are necessarily Markdown, ideally independently of whether or not non-doc comments are formatted.

Start by tracing the wrap_comments handling for doc comments and review the context in issue #627. The issue does not name files or tests, and proposes a general Markdown formatter used inside doc comments; done would include reflowing the shown comment while considering the stated behavior for non-doc comments.