Consolidate SAW documentation

[chameco]

Currently, there is a lot of tutorial (and some reference) material for SAW available in a bunch of different places, and discoverability is not ideal.
We should gather and assess the material we have, ensure it is consistent and up-to-date, and make it available in a common location.

[chameco]

Things that I'm aware of:

• the manual, available at https://saw.galois.com/manual.html
• the tutorial, available at https://saw.galois.com/tutorial.html
• saw-training, available at https://saw.galois.com/intro/
• saw-demos and this blog post that demonstrates using the Python frontend
• this series of blog posts walking through one of the s2n proofs?