See counterpart change resource-reasoning/jscert_dev@ae4f940

Expected comparison semantics were that +0<>-0, but JS === maps them to
the same value.

Add .ml implementation backed by Pervasives for ml JSRef' frontend.

ml2js wasn't including . in the include paths by default. Add flag for
explicitly indicating stdlib location.

Parse_type was partially taken from an old ocamldoc codebase which had a
conflicting license. Rewrite essentially from scratch, following the
structure of OCaml 4.03's driver/compile.ml `implementation` function.

Only changes to the ASTs required fixing:
* Asttypes.label -> Asttypes.arg_label
* New definition of Parsetree.constant, shadowing Asttypes.constant
* Addition of Typedtree.rec_flag
* Removal of Typedtree.optional

Required changes:
* Ignore ocaml.doc and ocaml.text attributes, which are now
  automatically extracted from comments.
* Swap type definition attribute syntax in test/* files.

Other changes:
* Add opam package file and `make init` command for dependencies.
* Change "Automatically Generated Attributes" documentation to comments.

Removes requirement for the compiler to be distributed with the
generator.
There is still a hard dependency on the precise OCaml version due to
syntactic changes between 4.02.1 and 4.02.2.