Don't allow equal signs in attr_list keys.

This will probably not result in the output intending by the author, but
the syntax would be incorrect so the author needs to edit the document
anyway. We just need to ensure the parser does not crash here. Fixes #498.

Author: waylan

markdown/extensions/attr_list.py

@@ -53,9 +53,9 @@ def _handle_word(s, t):
     return t, t
 
 _scanner = Scanner([
-    (r'[^ ]+=".*?"', _handle_double_quote),
-    (r"[^ ]+='.*?'", _handle_single_quote),
-    (r'[^ ]+=[^ =]+', _handle_key_value),
+    (r'[^ =]+=".*?"', _handle_double_quote),
+    (r"[^ =]+='.*?'", _handle_single_quote),
+    (r'[^ =]+=[^ =]+', _handle_key_value),
     (r'[^ =]+', _handle_word),
     (r' ', None)
 ])

tests/extensions/attr_list.html

@@ -65,4 +65,5 @@ <h1>Bad attributes</h1>
 <p><em>Weirdness</em></p>
 <p><em>More weirdness</em></p>
 <p>Attr_lists do not contain <em>newlines</em>{ foo=bar
-key=value }</p>
+key=value }</p>
+<p>Extra <em foo="bar">equals signs</em></p>

tests/extensions/attr_list.txt

@@ -90,3 +90,5 @@ No *key or value*{ = }
 
 Attr_lists do not contain *newlines*{ foo=bar
 key=value }
+
+Extra *equals signs*{ foo=bar=baz }