Add "J" (JSON) support to malloc_stats_print().

This resolves jemalloc#474.

Author: jasone

doc/jemalloc.xml.in

@@ -410,29 +410,30 @@ for (i = 0; i < nbins; i++) {
 	/* Do something with bin_size... */
 }]]></programlisting></para>
 
-      <para>The <function>malloc_stats_print()</function> function
-      writes human-readable summary statistics via the
-      <parameter>write_cb</parameter> callback function pointer and
-      <parameter>cbopaque</parameter> data passed to
-      <parameter>write_cb</parameter>, or
-      <function>malloc_message()</function> if
-      <parameter>write_cb</parameter> is <constant>NULL</constant>.  This
-      function can be called repeatedly.  General information that never
-      changes during execution can be omitted by specifying "g" as a character
+      <para>The <function>malloc_stats_print()</function> function writes
+      summary statistics via the <parameter>write_cb</parameter> callback
+      function pointer and <parameter>cbopaque</parameter> data passed to
+      <parameter>write_cb</parameter>, or <function>malloc_message()</function>
+      if <parameter>write_cb</parameter> is <constant>NULL</constant>.  The
+      statistics are presented in human-readable form unless <quote>J</quote> is
+      specified as a character within the <parameter>opts</parameter> string, in
+      which case the statistics are presented in <ulink
+      url="http://www.json.org/">JSON format</ulink>.  This function can be
+      called repeatedly.  General information that never changes during
+      execution can be omitted by specifying <quote>g</quote> as a character
       within the <parameter>opts</parameter> string.  Note that
       <function>malloc_message()</function> uses the
-      <function>mallctl*()</function> functions internally, so
-      inconsistent statistics can be reported if multiple threads use these
-      functions simultaneously.  If <option>--enable-stats</option> is
-      specified during configuration, &ldquo;m&rdquo; and &ldquo;a&rdquo; can
-      be specified to omit merged arena and per arena statistics, respectively;
-      &ldquo;b&rdquo;, &ldquo;l&rdquo;, and &ldquo;h&rdquo; can be specified to
-      omit per size class statistics for bins, large objects, and huge objects,
-      respectively.  Unrecognized characters are silently ignored.  Note that
-      thread caching may prevent some statistics from being completely up to
-      date, since extra locking would be required to merge counters that track
-      thread cache operations.
-      </para>
+      <function>mallctl*()</function> functions internally, so inconsistent
+      statistics can be reported if multiple threads use these functions
+      simultaneously.  If <option>--enable-stats</option> is specified during
+      configuration, <quote>m</quote> and <quote>a</quote> can be specified to
+      omit merged arena and per arena statistics, respectively;
+      <quote>b</quote>, <quote>l</quote>, and <quote>h</quote> can be specified
+      to omit per size class statistics for bins, large objects, and huge
+      objects, respectively.  Unrecognized characters are silently ignored.
+      Note that thread caching may prevent some statistics from being completely
+      up to date, since extra locking would be required to merge counters that
+      track thread cache operations.</para>
 
       <para>The <function>malloc_usable_size()</function> function
       returns the usable size of the allocation pointed to by