Update README

I made a few updates to the Building the Source section. This seems to have worked for me, but happy to change it if something is not quite right :)

* Turned "downloads area" into link to releases page
* Removed install albacore instruction
* Removed submodule init instruction (submodule pulled in 2ab0d50b59)
* Updated open solution instruction to VS2012 as sln file is 2012

Thanks!