Architecture documentation

[justinethier]

Create a markdown document explaining the overall architecture, and an explanation for each module. This should focus on the Scheme side since we do have some module docs for the C runtime.

[justinethier]

Much of this documentation has already been started. The best way to do this would probably be to refresh the Scheme API documentation for our internal modules, and create an up-to-date Architecture document based on the most recent "Writing the Cyclone Scheme Compiler" docs. Part of that would also be incorporating lazy sweeping into the comprehensive document.

[justinethier]

I suggest a simple architecture.md to handle this. We should be able to re-use some of the diagrams that were already put together for other documentation. Then it is a matter of documenting the high-level modules that are most important.

This document can link to other docs as needed, such as the "writing cyclone" and GC docs.

For background on what this new doc should look like see:

• https://matklad.github.io/2021/02/06/ARCHITECTURE.md.html
• https://github.com/rust-lang/rust-analyzer/blob/d7c99931d05e3723d878bea5dc26766791fa4e69/docs/dev/architecture.md