Add documentation examples for formatValue()

Add example showing how to forward format specifiers.
Add example highlighting the similarity with formattedWrite(), and
comparing their use.
The rule of thumb is: Minimize your commits, but have each commit contain only one logical change. Of course, if things get complicated, one huge commit is fine. The only thing is we try to avoid merging commits that are "Oops", "fix", "typo" etc...

During the process proper, you may or may not merge your commits as you go. Both ways have their advantages. Personally, I just like it when I make a comment, to be pinged when the comment is addressed.