This is a rewrite of the build system with `jbuilder`, with just a
minimal toplevel Makefile for backward compatibility.
This first patch preserves the project architecture, we only gain
proper dependencies handling and always up-to-date `.merlin` files.
A latter patch may split the project in smaller "sub-package",
i.e. multiple `.opam` files.
The embedded versions of the economic protocol are now compiled with
`jbuilder` instead of `tezos-protocol-compiler`, potentially allowing
proper inlining at the cost of slightly-less-stricter
sandboxing. Nevertheless, dynamically loaded protocol are still
compiled with the `tezos-protocol-compiler` and thus strictly
sandboxed ; and a CI rule also checks the proper sandboxing of
embedded protocols.
This patch is coauthored with @hnrgrgr
