Add text wrapping to HTML output.

Previously the HTML writer was exceptional in not being
sensitive to the `--wrap` option.  With this change `--wrap`
now works for HTML. The default (as with other formats) is
automatic wrapping to 72 columns.

A new internal module, T.P.Writers.Blaze, exports `layoutMarkup`.
This converts a blaze Html structure into a doclayout Doc Text.

In addition, we now add a line break between an `img` tag
and the associated `figcaption`.

Note: Output is never wrapped in `writeHtmlStringForEPUB`.
This accords with previous behavior since previously the HTML
writer was insensitive to `--wrap` settings.  There's no real
need to wrap HTML inside a zipped container.

Note that the contents of script, textarea, and pre tags are
always laid out with the `flush` combinator, so that unwanted
spaces won't be introduced if these occur in an indented context
in a template.

Closes #7764.

1 files changed, 2 insertions, 1 deletions

diff --git a/test/command/4186.md b/test/command/4186.md
index 90ac1271b..b2a2bd6e9 100644
--- a/test/command/4186.md
+++ b/test/command/4186.md
@@ -57,7 +57,8 @@ Outside all lists.
 </ul>
 <pre id="carrie" class="example"><code>This belongs to the outer list element, and is aligned accordingly, since the NAME attribute is not indented deeply enough. It is not enough for the BEGIN alone to be aligned deeply if the block is meant to have a NAME.
 </code></pre>
-<p>Still in the shallower list element since the preceding example block forced the deeper list element to terminate.</p></li>
+<p>Still in the shallower list element since the preceding example block
+forced the deeper list element to terminate.</p></li>
 </ul>
 <p>Outside all lists.</p>
 ```