New plugin file: scripts/lab.js.

lab.js is a file containing all the functions needed to implement hubot plugins for otrlab's slack chatroom. Til now, there are two commands in it:

    lab.echo XXX
    It will return XXX by hubot. This command is used to test whether hubot works correctly.

    lab.hackernews/lab.hn
    This command will return top 30 news on the Hackernews.com in the reversed order.
    Since the "hackernews.coffee' in the scripts provided by community is no longer maintained and it's easily broken in different environment, I implement with a third-party API of Hackernews.com