Update formatting lib, fix nuget binary reference

 *  Updates to a new version of F# formatting (it is marked as beta, but works nicely). Also, the new package now renames `content` folder with default styles to `styles` (so that the files are not automatically added to your solution by Visual Studio)

 * The paths in the `nuspec` file need to be relative to the nuspec folder (this is due to a recent change in FAKE).