Powershell build script and installer

A friendly to use Powershell script that automatically downloads from the web all tools needed to start using and building FAKE scripts (FSX).

I created this script to provide a self guiding install and build for FAKE, which allows for the user to quickly correct any configuration issues. I'm not sure if anyone else will find this useful or if it fits in with the vision of the project, but if it does great.  If it needs further work let me know and I will make further adjustments. 

This is my first pull request, so I hope I'm doing this right.