Simplify API provided to scriptcs scripts.

No longer need to import a script pack using Require.
Logging methods now available as global methods.
InstallPath, ToolsPath, Package, Project and DTE are now available
as global properties.
Host information is now available from a ScriptHost object.

    Log ("Running install.csx");

    Log ("ScriptHost.Name: " + ScriptHost.Name);
    Log ("ScriptHost.Version: " + ScriptHost.Version);
    Log ("NuGet version: " + ScriptHost.NuGetVersion.ToString());
    Log ("InstallPath: " + InstallPath);
    Log ("ToolsPath: " + ToolsPath);

    if (Package != null) {
    	Log ("Package.ToString (): " + Package.ToString ());
    }

    Log ("DTE.Version: " + DTE.Version);
    if (Project != null) {
    	Log ("Project.Name: " + Project.Name);
        DTE.ItemOperations.Navigate ("http://xamarin.com");
    }
Remove script packs.