This adopts a more guide-like writing style, similar to what prior commits
have done to some other subsections of this section.
Since we already have a whole top-level section devoted to modules, there
is no need for full coverage of all of their features here. Instead, this
section focuses on an an initial introduction to what modules are and
the basics of their usage within the Terraform language. We then link
to the main modules section for the full details.
The modules mechanism has changed quite a bit for version 0.11 and so
although simple usage remains broadly compatible there are some
significant changes in the behavior of more complex modules.
Since large parts of this were rewritten anyway, I also took the
opportunity to do some copy-editing to make the prose on this page more
consistent with our usual editorial voice and to wrap the long
lines.