Added threadName to LogRecord

Doc/lib/liblogging.tex

@@ -1268,6 +1268,7 @@ Currently, the useful mapping keys in a \class{LogRecord} are:
 \lineii{\%(msecs)d}    {Millisecond portion of the time when the
                         \class{LogRecord} was created.}
 \lineii{\%(thread)d}   {Thread ID (if available).}
+\lineii{\%(threadName)s}   {Thread name (if available).}
 \lineii{\%(process)d}  {Process ID (if available).}
 \lineii{\%(message)s}  {The logged message, computed as \code{msg \% args}.}
 \end{tableii}