Support jinja2-3.0

Since jinja2-3.0, some utility functions like contextfunction and
environmentfilter are renamed to new name.  This follows the updates to
support jinja2-3.0 or above.

setup.py

@@ -21,8 +21,7 @@ install_requires = [
     'sphinxcontrib-htmlhelp',
     'sphinxcontrib-serializinghtml',
     'sphinxcontrib-qthelp',
-    'Jinja2>=2.3,<3.0',
-    'MarkupSafe<2.0',
+    'Jinja2>=2.3',
     'Pygments>=2.0',
     'docutils>=0.14,<0.18',
     'snowballstemmer>=1.1',