add opengraph metadata to pages, via Markdown meta

tests/functional_tests.py

@@ -30,6 +30,15 @@ def test_page_without_title_metadata(client):
     assert b'<h1>this page doesn\'t have a title!</h1>' in response.data
 
 
+def test_page_with_card_metadata(client):
+    """Test that a page with opengraph metadata."""
+    response = client.get('/more-metadata')
+    assert response.status_code == 200
+    assert b'<meta property="og:title" content="title for the page">' in response.data
+    assert b'<meta property="og:description" content="description of this page">' in response.data
+    assert b'<meta property="og:image" content="http://buh.com/test.img">' in response.data
+
+
 def test_page_has_modified_timestamp(client):
     """Test that pages have modified timestamps in them."""
     response = client.get('/')

tests/instance/pages/more-metadata.md

@@ -0,0 +1,5 @@
+Title:          title for the page
+Description:    description of this page
+Image:          http://buh.com/test.img
+
+hello