#230 Improve Node.js tutorial examples

[Jira Trac]

I've received a feedback from a user who wants to use CUBRID Node.js driver. He says that at first sight, the example displayed in [README.md|https://github.com/CUBRID/node-cubrid/blob/master/Readme.md] on Github looks like spagetti.

He understands that calls follow *waterfall* flow, but since there are so many callbacks, the code simply looks not readable.

I'd like to suggest to change extract the callback function in a separated named functions. This would at least make it more readable.

We could also create an example which shows how to use CUBRID Node.js driver with [async|https://github.com/caolan/async] module.