This is just a beginning, but hopefully we can expand it with more
information and options, and then use it to get everybody in our
nascent FFI/RPC working group on the same page.
Specifically, I'm adding a high-level MDD (simplified for clarity).
I'm also adding a diagram of the object relations among our manager
types. (There are also communications that happen via channels, but
those aren't discussed here.) That part closes#624.
There is probably more to say here, but this should form a scaffold
we can build on.
This commit updates the crate list in Architecture.md. Because of the
previous commit, which introduced consistency to these files, it was
possible to generate it fairly easy with a tiny Perl script.