Lexer and parser for SimPL

Adapted from https://www.cs.cornell.edu/courses/cs3110/2021sp/textbook/interp/simpl_frontend.html

Migrated from ocamlbuild to dune, and from ocamllex to sedlex.

Notes

In dune, don't put sedlex_ppx in libraries as in the sedlex examples dune. It will fail to find it. Instead, put substitute it for ppxlib.

Links

• https://schu.be/til-sedlex-and-menhir.html
• https://github.com/jorisgio/menhir-workshop/
• https://github.com/sufrin/InteractiveSedlexMenhirExample
• https://github.com/ocaml-community/sedlex/tree/master/examples