Issue #2 - using GitHub API v3

Hi,

I solved [issue 2][1] by modifying the script to use the GitHub API v3. See more explanation [in the commit message][2].

I also converted the README into markdown.

[1]: https://github.com/enygma/offline-issues/issues/2
[2]: https://github.com/hcs42/offline-issues/commit/5649e6b608d217ccce6b0ce71b1647e15472c323