The previous implementation used global state and was making another
change more difficult than it had to be.
Note: I got rid of `rev_let_bound_idents` in the API because computing
it is no more efficient than `Fun.compose List.rev let_bound_idents`.
(Only the _full versions might have a more-efficient rev_ version,
and those are not exposed, which is the right choice:
a simpler API is worth a list reversal.)
* Various file moves in the middle end: this is the first stage of improving separation between the middle end and backend.
* Creation of file_formats/ directory (with associated file moves) to hold the definitions of compilation artifact formats.
* Creation of lambda/ directory (with associated file moves) to hold Lambda language definition files, transformation passes and construction passes from Typedtree.
* Disable (hopefully temporarily) dynlink, debugger and ocamldoc for the dune build.
Thomas Refis
Gabriel Scherer
Leo White
Mark Shinwell