Consolidate/reorganize the tutorials/documentation

[judah]

We have three tutorials: docs/tutorial.md, proto-lens-tutorial/person/Readme.md and proto-lens-tutorial/coffee-order/Readme.md. It's not exactly clear what the difference is between the three of them (or, for example, what order you should read them in). It's also a bit of maintenance burden to manage all three.

Additionally, we should consider distinguishing in-depth documentation of the library from "tutorials" which give a more basic introduction to the library.