Cleans up arthur to use the new monadic-let binding syntax.
Adds documentation for the CHECK interface, and it's derived sub interfaces.
Adds comments for the various checkers indicating what rules they check for.
Adds comments the arthur_parse folder.
Refactors the line-length testing (that we moved out to linter.ml temporarily for HW2) back into the CHECK interface, so that we can start ignoring these rules (but only at a global level).
^^ The above comments are docstring comments, meaning they are inserted into the docs that dune can generate.
This pr:
^^ The above comments are docstring comments, meaning they are inserted into the docs that dune can generate.