Don't auto link patterns surrounded by """.

This allows the prevention of `[WikiWikiWeb](http://wiki.c2.com/?WikiWikiWeb)`
being transformed to `<a href="http://wiki.c2.com/?&lt;a href=&quot;aw.cgi?page=WikiWikiWeb&quot;&gt;WikiWikiWeb&lt;/a&gt;">WikiWikiWeb</a>` when
the pattern linker sees the second WikiCase word by surrounding it with triple quotes: so `[WikiWikiWeb](http://wiki.c2.com/?"""WikiWikiWeb""")`
is now transformed to `<a href="http://wiki.c2.com/?WikiWikiWeb">WikiWikiWeb</a>`.

The function responsible, _do_link_patterns(), already checked for the cases that the pattern was inside square brackets, or
was preceeded by `](` or suffixed by `")`, and skips expanding in these cases. This addition simply adds a check that the pattern is not surrounded
by triple quotes; the triple quotes are stripped from the output.

lib/markdown2.py

@@ -1772,7 +1772,7 @@ def _code_block_sub(self, match, is_fenced_code_block=False):
                 lexer_name = lexer_name[3:].strip()
                 codeblock = rest.lstrip("\n")   # Remove lexer declaration line.
                 formatter_opts = self.extras['code-color'] or {}
-        
+
         # Use pygments only if not using the highlightjs-lang extra
         if lexer_name and "highlightjs-lang" not in self.extras:
             def unhash_code(codeblock):
@@ -2146,7 +2146,7 @@ def _encode_amps_and_angles(self, text):
     def _encode_incomplete_tags(self, text):
         if self.safe_mode not in ("replace", "escape"):
             return text
-            
+
         return self._incomplete_tags_re.sub("<\\1", text)
 
     def _encode_backslash_escapes(self, text):
@@ -2218,6 +2218,11 @@ def _do_link_patterns(self, text):
                 if text[start - 2:start] == '](' or text[end:end + 2] == '")':
                     continue
 
+                # Do not match against links which are escaped.
+                if text[start - 3:start] == '"""' and text[end:end + 3] == '"""':
+                    text = text[:start - 3] + text[start:end] + text[end + 3:]
+                    continue
+
                 escaped_href = (
                     href.replace('"', '"')  # b/c of attr quote
                         # To avoid markdown <em> and <strong>: