Cleaning up old code

Deletes almost everything not required to successfully `make` and build a new submarine.

I've left in `hub/` to allow urbit development to move forward, as well as `doc/` and some parts of `Spec/`. Not all of `Spec/` is up to date, but it has some useful facts about how the loom appears to work, the origins of Hoon (Watt), and possibly the correct Nock spec.

A lot of historically interesting code has been deleted, but it's probably best for someone new to Urbit to see primarily the code, pronunciations, and names that are being actively used. Once I (or someone else) have a better grasp of how Hoon and Nock play in the reference implementation, it would be advantageous to clean up Spec/ to be both interesting and relevant.