#233: Adding ability to put pid in log layout pattern

lib/layouts.js

@@ -125,6 +125,7 @@ function messagePassThroughLayout (loggingEvent) {
  *  - %d date in various formats
  *  - %% %
  *  - %n newline
+ *  - %z pid
  *  - %x{<tokenname>} add dynamic tokens to your log. Tokens are specified in the tokens parameter
  * You can use %[ and %] to define a colored block.
  *
@@ -211,6 +212,10 @@ function patternLayout (pattern, tokens) {
     return '%';
   }
 
+  function pid() {
+    return process.pid;
+  }
+
   function userDefined(loggingEvent, specifier) {
     if (typeof(tokens[specifier]) !== 'undefined') {
       if (typeof(tokens[specifier]) === 'function') {
@@ -232,6 +237,7 @@ function patternLayout (pattern, tokens) {
     'r': startTime,
     '[': startColour,
     ']': endColour,
+    'z': pid,
     '%': percent,
     'x': userDefined
   };