Just to be clear, the "stable" version *is* version 3.0. Perhaps you are looking for the current development version, which is the most up to date (some new functionality since "stable")? If you want to use the all in one installation, there are directions on our web page:
http://yt-project.org/#getyt and in the docs here:
http://yt-project.org/docs/dev/installing.html#all-in-one-installation-script . I see that it only has the link in the docs for getting the "stable" install_script, but if you want the "development" install_script, it's this instead:
I'll change the docs to make this more clear to future users. I hope this helps!