[tuple, variant] Turn synopses into numbered subclauses

In pursuit of issue #566.

Author: tkoeppe

source/utilities.tex

@@ -1400,10 +1400,9 @@
 two arguments is similar to an instantiation of \tcode{pair} with the same two arguments.
 See~\ref{pairs}.
 
-\pnum
-\synopsis{Header \tcode{<tuple>} synopsis}
+\rSec2[tuple.syn]{Header \tcode{<tuple>} synopsis}
+\indexlibrary{\idxhdr{tuple}}
 
-\indexlibrary{\idxhdr{tuple}}%
 \begin{codeblock}
 namespace std {
   // \ref{tuple.tuple}, class template \tcode{tuple}
@@ -2512,8 +2511,8 @@
 object is tracked by the optional object.
 
 \rSec2[optional.syn]{Header \tcode{<optional>} synopsis}
+\indexlibrary{\idxhdr{optional}}
 
-\indexlibrary{\idxhdr{optional}}%
 \begin{codeblock}
 namespace std {
   // \ref{optional.optional}, optional
@@ -3989,8 +3988,8 @@
 of the template argument types given to variant.
 These template arguments are called alternatives.
 
-\indexlibrary{\idxhdr{variant}}%
-\synopsis{Header \tcode{<variant>} synopsis}
+\rSec2[variant.syn]{Header \tcode{<variant>} synopsis}
+\indexlibrary{\idxhdr{variant}}
 
 \begin{codeblock}
 namespace std {
@@ -4002,8 +4001,8 @@
   template <class T> struct variant_size<const T>;
   template <class T> struct variant_size<volatile T>;
   template <class T> struct variant_size<const volatile T>;
-  template <class T> constexpr size_t variant_size_v
-    = variant_size<T>::value;
+  template <class T>
+    constexpr size_t variant_size_v = variant_size<T>::value;
 
   template <class... Types>
     struct variant_size<variant<Types...>>;