helper method to call process exit

[Shwetajain148]

@mchaudhary, @mostlyjason, I have created and exposed the flushLogsAndExit method to call process.exit() after 10 seconds. Users can call this method to call process.exit internally after 10 seconds.

They will need to do something like below in their app.js file:

var winston = require('winston'),
winlog = require('winston-loggly-bulk');

winlog.flushLogsAndExit();

[Shwetajain148]

Fix of #19