FastCGI implementation in OCaml

This branch exists to figure out an OCaml specification for the FastCGI interface.

The spec for the FastCGI protocol is in spec/FastCGI_Specification.html. The Go lang implementation of FastCGI is in spec/fcgi.go.

Both of these are intended to act as a reference implementation, for us to figure out what the ideal OCaml interface should look like for FastCGI.

Our target language is OCaml, using the Eio library. The README for Eio is in OCaml-EIO-README.md to give you a reference.