I am not currently set up to work with Tiny13 so the development is on hold. At this point, it is best just to use one of the forks. There are a number of differences -- some are clearly improvements and others have upsides and downsides. Either way, you could always transplant bits of code if it doesn't work exactly how you want. The important thing is that they are maintained to be compatible with the newest version of the Arduino IDE. Something I always had trouble with because it changes so often