Switch minimum version to OCaml 4.02.2 (maximum version <4.03)

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.