[stacktrace.format], [stacktrace.basic.hash] change rSec3 to rSec2

These should not be nested below std::basic_stacktrace because they
apply to both std::stacktrace_entry and std::basic_stacktrace.

Author: jwakely

source/diagnostics.tex

@@ -2400,7 +2400,7 @@
 Equivalent to: \tcode{return os << to_string(st);}
 \end{itemdescr}
 
-\rSec3[stacktrace.format]{Formatting support}
+\rSec2[stacktrace.format]{Formatting support}
 
 \begin{itemdecl}
 template<> struct formatter<stacktrace_entry>;
@@ -2442,7 +2442,7 @@
 copying \tcode{to_string(s)} through the output iterator of the context.
 \end{itemdescr}
 
-\rSec3[stacktrace.basic.hash]{Hash support}
+\rSec2[stacktrace.basic.hash]{Hash support}
 
 \begin{itemdecl}
 template<> struct hash<stacktrace_entry>;