Very Basic PR

Hi, @dinhviethoa,
I just wrote some basic stuffs(most on structure) and could you please review my source codes, if i make some errors, let me know.

Otherwise, this PR also is a complete PR but within some TODO for us, So you could run the `example.js` to check the functionality of mine.

Also /cc @MailCore's other members :)
Could you move this file to a folder named example/?
and name this file simple-imap-fetch.js or a name different from example.js.