added an example for logging

+phantom.injectJs('casper.js');
+var casper = new phantom.Casper({
+    verbose: true,
+    logLevel: 'debug'
+})
+casper.log('this is a debug message', 'debug');
+casper.log('and an informative one', 'info');
+casper.log('and a warning', 'warning');
+casper.log('and an error', 'error');
+casper.exit();