Support >3 backticks in github-flavored fences.

mkcodes.py

@@ -29,7 +29,7 @@ def default_state():
 def github_codeblocks(filename, safe):
     codeblocks = []
     codeblock_re = r'^```.*'
-    codeblock_open_re = r'^```(py|python){0}$'.format('' if safe else '?')
+    codeblock_open_re = r'^```(`*)(py|python){0}$'.format('' if safe else '?')
 
     with open(filename, 'r') as f:
         block = []

tests/data/some.md

@@ -13,3 +13,9 @@ bar = False
 Some daring-fireball-flavored code:
 
     baz = None
+
+More than 3 backticks is allowed:
+
+`````py
+backticks = range(5, 7)
+```````

tests/test.py

@@ -39,6 +39,9 @@ def test_github_safe(self):
         self.call('--github', '--safe')
         self.assertOutput("""\
             bar = False
+
+
+            backticks = range(5, 7)
             """)
 
     def test_markdown_unsafe(self):
@@ -54,6 +57,9 @@ def test_github_unsafe(self):
 
 
             bar = False
+
+
+            backticks = range(5, 7)
             """)
 
 
@@ -77,6 +83,9 @@ def test_multiple(self):
                 'tests/data/some.md', 'tests/data/other.md'])
             self.assertFileEqual('tests/some.py', """\
                 bar = False
+
+
+                backticks = range(5, 7)
                 """)
             self.assertFileEqual('tests/other.py', """\
                 qux = 4