Merge finished proposals

The following proposals are marked FINISHED, meaning that they have been built, but not merged into the main specs. We should finish them.

• 260-rend-single-onion.txt: Rendezvous Single Onion Services (Finished)
• 332-ntor-v3-with-extra-data.md: Ntor protocol with extra data, version 3. (Finished) See !163 (merged).
• 333-vanguards-lite.md: Vanguards lite (Finished)

@mikeperry @dgoulet I can do 332. If you want to merge 360 and 333 that would be great, but if not it would be cool if you could spare the time to look them over to see whether they are accurate and need any changes to describe what Tor actually does. Once that is done, I can merge them if you don't have time.