Move DD code into its own directory (#6)

reference/ddtrace/utils/http.py

@@ -0,0 +1,9 @@
+def normalize_header_name(header_name):
+    """
+    Normalizes an header name to lower case, stripping all its leading and trailing white spaces.
+    :param header_name: the header name to normalize
+    :type header_name: str
+    :return: the normalized header name
+    :rtype: str
+    """
+    return header_name.strip().lower() if header_name is not None else None