Use R.NET 1.5.13 packages on nuget.org

use more recent, publicly available [R.NET packages at nuget.org](https://www.nuget.org/packages/R.NET.Community). Includes the latest changes on the fork of @dcharbon and the current master branch of the Blue Mountain Capital repository. Could compile the projects in the solutions, and run/pass the unit tests. I am not familiar enough with Fake to gauge whether I need to do something there.