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>

tests/test_escaping.py

@@ -12,7 +12,7 @@ def test_underscore():
 
 
 def test_xml_entities():
-    assert md('&') == '&'
+    assert md('&') == r'\&'
 
 
 def test_named_entities():
@@ -25,4 +25,23 @@ def test_hexadecimal_entities():
 
 
 def test_single_escaping_entities():
-    assert md('&') == '&'
+    assert md('&') == r'\&'
+
+
+def text_misc():
+    assert md('\\*') == r'\\\*'
+    assert md('<foo>') == r'\<foo\>'
+    assert md('# foo') == r'\# foo'
+    assert md('> foo') == r'\> foo'
+    assert md('~~foo~~') == r'\~\~foo\~\~'
+    assert md('foo\n===\n') == 'foo\n\\=\\=\\=\n'
+    assert md('---\n') == '\\-\\-\\-\n'
+    assert md('+ x\n+ y\n') == '\\+ x\n\\+ y\n'
+    assert md('`x`') == r'\`x\`'
+    assert md('[text](link)') == r'\[text](link)'
+    assert md('1. x') == r'1\. x'
+    assert md('not a number. x') == r'not a number. x'
+    assert md('1) x') == r'1\) x'
+    assert md('not a number) x') == r'not a number) x'
+    assert md('|not table|') == r'\|not table\|'
+    assert md(r'\ <foo> &amp;amp; | ` `', escape_misc=False) == r'\ <foo> &amp; | ` `'