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>

markdownify/__init__.py

@@ -71,6 +71,7 @@ class MarkdownConverter(object):
         default_title = False
         escape_asterisks = True
         escape_underscores = True
+        escape_misc = True
         heading_style = UNDERLINED
         keep_inline_images_in = []
         newline_style = SPACES
@@ -201,6 +202,9 @@ class MarkdownConverter(object):
     def escape(self, text):
         if not text:
             return ''
+        if self.options['escape_misc']:
+            text = re.sub(r'([\\&<`[>~#=+|-])', r'\\\1', text)
+            text = re.sub(r'([0-9])([.)])', r'\1\\\2', text)
         if self.options['escape_asterisks']:
             text = text.replace('*', r'\*')
         if self.options['escape_underscores']: