Update fetch scripts to download NUnit 3.0.1, and adjust paths

Update Makefile to look for nunit3-console.exe

thirdparty/fetch-thirdparty-deps.ps1

@@ -62,7 +62,7 @@ if (!(Test-Path "SharpFont.dll"))
 if (!(Test-Path "nunit.framework.dll"))
 {
 	echo "Fetching NUnit from NuGet."
-	./nuget.exe install NUnit -Version 2.6.4 -ExcludeVersion
+	./nuget.exe install NUnit -Version 3.0.1 -ExcludeVersion
 	cp NUnit/lib/nunit.framework* .
 	rmdir NUnit -Recurse
 }