Add support for \begin foo \end math blocks

IPython/nbconvert/filters/markdown.py

@@ -72,9 +72,10 b' def markdown2latex(source):'
 
 class MathBlockGrammar(mistune.BlockGrammar):
     block_math = re.compile("^\$\$(.*?)\$\$")
+    block_math2 = re.compile(r"^\\begin(.*?)\\end")
 
 class MathBlockLexer(mistune.BlockLexer):
-    default_features = ['block_math'] + mistune.BlockLexer.default_features
+    default_features = ['block_math', 'block_math2'] + mistune.BlockLexer.default_features
 
     def __init__(self, rules=None, **kwargs):
         if rules is None:
@@ -88,6 +89,8 b' class MathBlockLexer(mistune.BlockLexer):'
             'text': m.group(1)
         })
 
+    parse_block_math2 = parse_block_math
+
 class MathInlineGrammar(mistune.InlineGrammar):
     math = re.compile("^\$(.+?)\$")