Switch build system from ocamlbuild to dune

[nomeata]

• There is still a Makefile to offer convenient targets, like

  make
  make all
  make asc
  make didc
  

• All ml files are in subdirectories of src/.
  See the file Structure.md for more details.

  This PR does not yet split the files into more subdirectories than
  necessary.

  There is a lib/ library, to show what is possible, and the
  executables are in their own directory, which is necessary, but
  otherwise all files are in aslib and idllib.

  I will split aslib into more sane components in a separte PR.

• We lose the coverage report that noone has looked at.
  Once How to support bisect_ppx? ocaml/dune#57 looks more promising
  we can add it back.

• Warnings are no longer fatal when using make (you still see them);
  building with nix-build (and hence CI) will fail if warnings
  remain. I think this gives a nicer development experience.

• Moved build (hardly changes) instructions to Building.md, so that
  Readme.md starts again with Goals, and describes the language.

[crusso]

@joachim, ok, I checked out your branch. nix-build works fine, I think, but I get an error when I do nix-shell following by make clean and make in src:

crusso@crusso-Virtual-Machine:~/actorscript$ nix-build
/nix/store/kyf013gmvc2qp3b2ic1v8a3q9r9a4kvv-all-systems-go
/nix/store/16p20sr8m50z1ycgbj03570a3m8ik4xk-asc
/nix/store/bwhw2359lchqdc5c844idf30627n504n-asc-bin
/nix/store/7k84i7xy04fjckaqfwh8jks9c1v0a4lm-dfinity-dvm-0.0.0
/nix/store/vd609f0b05xsgzw729kqc3dywhlgjs48-FileCheck
/nix/store/2a1z8r6y9jqggz454xy48m3gp0bfjy5p-didc
/nix/store/z2spmr3v2dy645nvhwjaivg04c41b2l6-asc.js
/nix/store/5s2chhcfjdzz0hby9051zpagydszfp97-produce-exchange
/nix/store/9y3h2qw2l2x4pdgbhs6pl72l9mh2xx35-asc-rts
/nix/store/rp5lx6l2797yn02wdlz4i99k53q7z2k6-stdlib-reference
/nix/store/2xjq34asx4zmray7df6nvw8gffbm0x55-tests
/nix/store/m3kjvycrimrd4hgbnv8dz23wc4sgb4zb-users-guide
/nix/store/ir9b9kh0wsh3nisy2s3fy5vh46dxilsx-wabt-1.0.8
/nix/store/9warm1jp69svybxc0pfr644rgz0l1myc-ocaml4.06.1-wasm-1.0
crusso@crusso-Virtual-Machine:~/actorscript$ nix-shell

[nix-shell:~/actorscript]$ cd src

[nix-shell:~/actorscript/src]$ make clean
rm -f asc as-ld asc.js didc
dune clean

[nix-shell:~/actorscript/src]$ make
dune build  _build/default/exes/as_ld.exe _build/default/exes/asc.exe _build/default/exes/as_js.bc.js _build/default/exes/didc.exe
File "exes/dune", line 20, characters 18-33:
20 |  (preprocess (pps js_of_ocaml-ppx))
                       ^^^^^^^^^^^^^^^
Error: Library "js_of_ocaml-ppx" not found.
Hint: try: dune external-lib-deps --missing _build/default/exes/as_ld.exe _build/default/exes/asc.exe _build/default/exes/as_js.bc.js _build/default/exes/didc.exe
make: *** [Makefile:19: all] Error 1

[nix-shell:~/actorscript/src]$ 

[nomeata]

Thanks, fixed!

[crusso]

Thanks for biting the bullet.

[rossberg]

Why remove all the test targets? I was using them.

[nomeata]

Right, forgot to explain this in the bullet point above: I has always bothered me that make in src/ does something in a test/. When I run make in src/ I want to build stuff in src (only).

If you want a single “build-all-and-test-all” command, and nix-build does not cut it, and make -C src && make -C test doesn’t either, then I advocate for a top-level Makefile.