Make \end{XXX} match the correct environment name

With this a \end{XXX} tag only matches a \begin{...} tag with the same
environment name. Effectively,

    \begin{equation*}
      I = \begin{pmatrix}
	1 & 0\\
	0 & 1
      \end{pmatrix}
    \end{equation*}

won't result in borked syntax.

Author: Gautam Iyer

mdx_math.py

@@ -28,10 +28,11 @@ def handle_match_inline(m):
         def handle_match(m):
             node = markdown.util.etree.Element('script')
             node.set('type', 'math/tex; mode=display')
-            node.text = markdown.util.AtomicString(m.group(3))
             if '\\begin' in m.group(2):
                 node.text = markdown.util.AtomicString(m.group(2) +
-                m.group(3) + m.group(4))
+		    m.group(4) + m.group(5))
+	    else:
+		node.text = markdown.util.AtomicString(m.group(3))
             return node
 
         configs = self.getConfigs()
@@ -42,7 +43,7 @@ def handle_match(m):
         mathpatterns = (
             markdown.inlinepatterns.Pattern(r'(?<!\\)(\$\$)([^\$]+)(\$\$)'), # $$...$$
             markdown.inlinepatterns.Pattern(r'(?<!\\)(\\\[)(.+?)(\\\])'),    # \[...\]
-            markdown.inlinepatterns.Pattern(r'(?<!\\)(\\begin{[a-z]+\*?})(.+)(\\end{[a-z]+\*?})')
+            markdown.inlinepatterns.Pattern(r'(?<!\\)(\\begin{([a-z]+?\*?)})(.+?)(\\end{\3})')
         )
         if not configs['enable_dollar_delimiter']:
             inlinemathpatterns = inlinemathpatterns[1:]