Need a design document

[eeeebbbbrrrr]

We need to document, in detail, what postgrestd is.

I'm thinking answering the typical, who, what, when, where, why, and how questions, along with things like

• which parts of the Rust standard library does postgrestd change? Perhaps a table that lists the changes, and details why for each one
• why does postgrestd take over allocation and pass it through to Postgres. What does this mean for Rust drop semantics, Rust lifetime management, etc
• how are Rust panics!()s handled

I don't feel qualified to even begin to outline this, so @workingjubilee, welcome to the party! 🎉