Refactor console logging code.

Util.Debug, Util.Info, Util.Warn, Util.Error routines instead of
direct calls to console.*. Add "logging=XXX" query variable that sets
the logging level (default is "warn").

Logging values:
    debug: code debug logging (many calls in performance path are also
           commented for performance reasons).
    info: informative messages including timing information.
    warn: significant events
    error: something has gone wrong

include/base64.js

@@ -111,7 +111,7 @@ decode: function (data, offset) {
         var padding = (data.charAt(i) == pad);
         // Skip illegal characters and whitespace
         if (c == -1) {
-            console.log("Illegal character '" + data.charCodeAt(i) + "'");
+            console.error("Illegal character '" + data.charCodeAt(i) + "'");
             continue;
         }