Layer 2 and Azimuth docs

[drbeefsupreme]

This draft PR will be used to add layer 2 documentation as it is written.

At the moment there are 2 new pages: /azimuth/layer2.md and
/azimuth/l2-actions.md.

layer2.md is a broad overview of how naive.hoon works intended for
developers. Some of it is about the aggregator, which will eventually be split
off into its own document. Yet to be added is an explanation of the byte format of
a L2 transaction and the form of a signed transaction. I am open to suggestions
for what else might be useful there.

l2-actions.md is a list of what L2 actions are available to each (rank, dominion)
tuple. This is complete, but there may be room for improvement in the
formatting.

Parts yet to be written in order of priority:

Bridge documentation intended for end-users
How to extract L2 PKI state tutorial
HTTP API documentation
Explainer for what all the different parts do and how data moves between them
How to set up an aggregator tutorial

I'm aiming to have the first two complete by the time L2 launches (though expect
to complete more). The HTTP API
documentation already mostly exists, its just not in a form suitable for
urbit.org. Same with the explainer on what all the different parts do.

[philipcmonk]

This is great documentation. Some time we should write docs at a similar level for layer 1.

[drbeefsupreme]

I've made the edits you asked @philipcmonk but won't be able to post the commit until later tonight when I'm at my own computer.

[drbeefsupreme]

As I write these docs its becoming more obvious that I should just explain Azimuth as a whole, including layer 1. l2-flow.md is the start of this. Since I don't know Solidity I don't know that I'll actually cover how the smart contracts work and will just focus on the Urbit side of things, but if I can scrape by with a really basic understanding then I'll try to do that as well.

[tinnus-napbus]

LGTM, just a few minor nits. Impressively comprehensive.

[drbeefsupreme]

This PR is ready to be merged.

I removed the link to @yosoyubik 's roller API docs since they're out of date. We can add them back in at a later date once he updates them. 48558a5