Escape all characters with Markdown significance (#118)

* Escape all characters with Markdown significance

There are many punctuation characters that sometimes have significance
in Markdown; more systematically escape them all (based on a new
escape_misc configuration option).

A limited attempt is made to limit the escaping of '.' and ')' to the
context where they might have Markdown significance (after a number,
where they can indicate an ordered list item); no such attempt is made
for the other characters (and even that limiting of '.' and ')' may
not be entirely safe in all cases, as it's possible the HTML could
have the number outside the block being escaped in one go,
e.g. `<span>1</span>.`.

---------

Co-authored-by: AlexVonB <AlexVonB@users.noreply.github.com>

README.rst

@@ -123,6 +123,11 @@ escape_underscores
   If set to ``False``, do not escape ``_`` to ``\_`` in text.
   Defaults to ``True``.
 
+escape_misc
+  If set to ``False``, do not escape miscellaneous punctuation characters
+  that sometimes have Markdown significance in text.
+  Defaults to ``True``.
+
 keep_inline_images_in
   Images are converted to their alt-text when the images are located inside
   headlines or table cells. If some inline images should be converted to