feat: Renderer add interim references with default values

renderer/references.py

@@ -0,0 +1,15 @@
+import re
+
+from mistletoe.span_token import SpanToken
+
+
+class References(SpanToken):
+    """
+    Resolve references for html
+    Identifies "[ref:$]"
+    """
+    pattern = re.compile(r"\[ref\:(\S+)\]")
+
+    def __init__(self, match_object):
+        self.first = match_object.group(1)
+