Updated Logger.log() documentation to clarify that lvl parameter should be an integer.

Doc/lib/liblogging.tex

@@ -314,7 +314,7 @@ The arguments are interpreted as for \method{debug()}.
 \end{methoddesc}
 
 \begin{methoddesc}{log}{lvl, msg\optional{, *args\optional{, **kwargs}}}
-Logs a message with level \var{lvl} on this logger.
+Logs a message with integer level \var{lvl} on this logger.
 The other arguments are interpreted as for \method{debug()}.
 \end{methoddesc}