Describe options.logger, enable syntax highlighting

Fixes #40.

README.md

@@ -17,31 +17,39 @@ This year as work content change, I have no spare time to maintaining the node m
 
 To use the logger:
 
-    app.use(require('express-bunyan-logger')());
+```js
+app.use(require('express-bunyan-logger')());
+```
 
 To use the errorLogger:
 
-    app.use(require('express-bunyan-logger').errorLogger());
+```js
+app.use(require('express-bunyan-logger').errorLogger());
+```
 
 And you can also pass bunyan logger options to the logger middleware:
 
-    app.use(require('express-bunyan-logger')({
-        name: 'logger',
-        streams: [{
-            level: 'info',
-            stream: process.stdout
-            }]
-        }));
+```js
+app.use(require('express-bunyan-logger')({
+    name: 'logger',
+    streams: [{
+        level: 'info',
+        stream: process.stdout
+    }]
+}));
+```
 
 Change default format:
 
-    app.use(require('express-bunyan-logger')({
-        format: ":remote-address - :user-agent[major] custom logger"
-    });
+```js
+app.use(require('express-bunyan-logger')({
+    format: ":remote-address - :user-agent[major] custom logger"
+});
+```
 
 And a child logger will be attached to each request object:
 
-```javascript
+```js
 app.use(require('express-bunyan-logger')();
 app.use(function(req, res, next) {
     req.log.debug('this is debug in middleware');
@@ -51,6 +59,10 @@ app.use(function(req, res, next) {
 
 ## Configuration
 
+### options.logger
+
+A custom instance of `bunyan` logger to use in the middware. Useful if you already do all of the logging with `bunyan` and don't want this middleware to create a new unconfigured instance. Also useful if you want to pass a child logger into this middleware.
+
 ### options.format
 
 Format string, please go the source code to the metadata. ":name" will print out meta.name; ":name[key]" will print out the property 'key' of meta.name.
@@ -65,7 +77,7 @@ Whether to parse _user-agent_ in logger, default is =true=.
 
 Function that translate statusCode into log level. The `meta` argument is an object consisting of all the fields gathered by bunyan-express-logger, before exclusions are applied.
 
-```
+```js
 function(status, err /* only will work in error logger */, meta) {
      // return string of level
      if (meta["response-time"] > 30000) {
@@ -80,7 +92,7 @@ function(status, err /* only will work in error logger */, meta) {
 
 Function that is passed `req` and `res`, and returns an object whose properties will be added to the meta object passed to bunyan
 
-```javascript
+```js
 function(req, res) {
     if (req.user) {
         return {
@@ -110,7 +122,7 @@ Default is `[HIDDEN]`.
 
 An object of [bunyan serializers](https://github.com/trentm/node-bunyan#serializers). They are passed on to bunyan.
 The default serializers are defined as follows:
-```
+```js
 {
     req: bunyan.stdSerializers.req,
     res: bunyan.stdSerializers.res,
@@ -128,7 +140,7 @@ By default, `express-bunyan-logger` will generate an unique id for each request,
 
 If you have already use other middleware/framework to generate request id, you can pass a function to retrieve it:
 
-```javascript
+```js
 // suppose connect-requestid middleware is already added.
 app.use(require('express-bunyan-logger')({
     genReqId: function(req) {