Merge pull request #1 from pankajksharma/master

Pankaj bhai created a userscript.

It now needs to be tested on Chrome and that's it.
Merge pull request #2 from pankajksharma/master

The userscript now works on Chrome and Safari too. 

Thanks again, @pankajsharma
Content-Length of Zip instead of GH API + Updated Readme.

Script now uses 'Content-Length' header of the Zip file, so the exact
size of the Zip file is shown (rounded to on decimal place.)

I'd also like to point out that the zip file is not actually downloaded,
only its size is fetched.
Some fix-ups in the Readme