Add normative references to ISO 8601 and RFC 6557, referenced

normatively by P0355R7.

Fixes #1971.

Author: zygoloid

source/intro.tex

@@ -35,8 +35,18 @@
 \begin{itemize}
 \item Ecma International, \doccite{ECMAScript Language Specification},
 Standard Ecma-262, third edition, 1999.
+%%% Format for this entry is based on that specified at
+%%% http://www.iec.ch/standardsdev/resources/draftingpublications/directives/principles/referencing.htm
+\item INTERNET ENGINEERING TASK FORCE (IETF). RFC 6557:
+Procedures for Maintaining the Time Zone Database [online].
+Edited by E. Lear, P. Eggert.
+February 2012 [viewed 2018-03-26].
+Available at
+\url{https://www.ietf.org/rfc/rfc6557.txt}
 \item ISO/IEC 2382 (all parts), \doccite{Information technology ---
 Vocabulary}
+\item ISO 8601:2004, \doccite{Data elements and interchange formats ---
+Information interchange --- Representation of dates and times}
 \item ISO/IEC 9899:2011, \doccite{Programming languages --- C}
 \item ISO/IEC 9945:2003, \doccite{Information Technology --- Portable
 Operating System Interface (POSIX)}

source/utilities.tex

@@ -26192,9 +26192,7 @@
 
 \pnum
 \ref{time.zone} describes an interface for accessing
-the IANA Time Zone database%
-%%% FIXME: Move URL to normative references
-\footnote{RFC 6557 https://tools.ietf.org/html/rfc6557},
+the IANA Time Zone database described in RFC 6557,
 that interoperates with \tcode{sys_time} and \tcode{local_time}.
 This interface provides time zone support to
 both the civil calendar types\iref{time.cal}