Avoid Markdown 2.6 deprecations; make MD_EXTENSIONS a dict

* Make MD_EXTENSIONS setting a dict and add tests for this change;
* Short extension names ('extra', 'meta') are deprecated
  https://pythonhosted.org/Markdown/release-2.6.html#shortened-extension-names-deprecated
* Extension config as part of extension name is deprecated
  https://pythonhosted.org/Markdown/release-2.6.html#extension-configuration-as-part-of-extension-name-deprecated

pelican/tests/test_pelican.py

@@ -207,3 +207,19 @@ class TestPelican(LoggedTestCase):
             count=2,
             msg="Writing .*",
             level=logging.INFO)
+
+    def test_md_extensions_list_deprecation(self):
+        """Test that a warning is issued if MD_EXTENSIONS is a list"""
+        settings = read_settings(path=None, override={
+            'PATH': INPUT_PATH,
+            'OUTPUT_PATH': self.temp_path,
+            'CACHE_PATH': self.temp_cache,
+            'MD_EXTENSIONS': ['meta'],
+        })
+        pelican = Pelican(settings=settings)
+        mute(True)(pelican.run)()
+        self.assertIsInstance(pelican.settings['MD_EXTENSIONS'], dict)
+        self.assertLogCountEqual(
+            count=1,
+            msg="The format of the MD_EXTENSIONS setting has changed",
+            level=logging.WARNING)

pelican/tests/test_readers.py

@@ -471,7 +471,12 @@ class MdReaderTest(ReaderTest):
         # expected
         page = self.read_file(
             path='article_with_markdown_markup_extensions.md',
-            MD_EXTENSIONS=['toc', 'codehilite', 'extra'])
+            MD_EXTENSIONS={
+                'markdown.extensions.toc': {},
+                'markdown.extensions.codehilite': {},
+                'markdown.extensions.extra': {}
+            }
+        )
         expected = ('<div class="toc">\n'
                     '<ul>\n'
                     '<li><a href="#level1">Level1</a><ul>\n'