Proposal to remove directories from source nuget package

Prior to this change, the source nuget package works in VS2012 and VS2013, but creates an awkward directory structure.  It doesn't work in Xamarin Studio without reordering the files, which is awkward since the directory structure means you can't drag and drop the files (at least in current XS5 Stable)

After this change, the source nuget package works in VS2012 and VS2013 and no directories are created.  In Xamarinn Studio the files are in the wrong order, but it's reasonably easier to reorder them since there are no directories in the way.

So this improves things in all the major F# editors supporting the addition of nuget source packages.