[time.general] Add a reference to time.hash in the summary

[time.general] has a library summary with references to the various
subclauses; [time.hash] was missing, add it.

source/time.tex

@@ -20,7 +20,8 @@
 \ref{time.12}               & 12/24 hour functions               & \\
 \ref{time.zone}             & Time zones                         & \\
 \ref{time.format}           & Formatting                         & \\
-\ref{time.parse}            & Parsing                            & \\ \rowsep
+\ref{time.parse}            & Parsing                            & \\
+\ref{time.hash}             & Hash support                       & \\ \rowsep
 \ref{ctime.syn}             & C library time utilities           & \tcode{<ctime>} \\
 \end{libsumtab}