Added threading example with requests. Also added 'from atpbar import…

[choudhary-archit]

… atpbar' in the previous example.

I recently used the atpbar module in a script of mine to download files from the internet concurrently using requests, and it was slightly nontrivial; the progress bar only updated after each iteration, so one had to break out of the buffering loop every time the progress bar was to be updated. I thought it would be a useful illustration of how to use atpbar.

Also in the threading example, only flush was import from atpbar, and not the atpbar.atpbar function. I changed this as well.

Thanks for making this module, it was very helpful since the other modules didn't seem to work in my script.