[thread.sharedmutex.class] Formatting fixes.

Author: zygoloid

source/threads.tex

@@ -1430,7 +1430,7 @@
 \throws Nothing.
 \end{itemdescr}
 
-\rSec4[thread.sharedmutex.class]{Class shared_mutex}
+\rSec4[thread.sharedmutex.class]{Class \tcode{shared_mutex}}
 
 \indexlibrary{\idxcode{shared_mutex}}%
 \begin{codeblock}
@@ -1444,12 +1444,12 @@
     shared_mutex& operator=(const shared_mutex&) = delete;
 
     // Exclusive ownership
-    void lock();    // blocking
+    void lock();                // blocking
     bool try_lock();
     void unlock();
 
     // Shared ownership
-    void lock_shared(); // blocking
+    void lock_shared();         // blocking
     bool try_lock_shared();
     void unlock_shared();