Update Install Documentation (Version Numbers)

Updates a couple of links and version numbers in the install documentation:

- OpenMPI 1.5.1+ including GPU-aware link #438
- boost 1.56/1.57 support since #593
- update link to new *official* pngwriter repo on GitHub
I was suprised by that some days ago, too and wrote that to nvidia.

I will change the link to `http://` in the mean time, I thought the complete webpage is down :)