Support for grader code reuse

[adhameer]

We have a lot of functions that we are using repeatedly across graders for different exercises. Currently we have to just copy and paste those functions into test.ml for each grader since we don't have control over the build. It would be very nice if we could just put all this code into a separate module and link it during compilation.

(Maybe there is already a way to do this, but if there is, I'm not sure how.)

[yurug]

As far as I know, there is no way to do that in the current version. This is a good idea! Thanks!

[Niols]

I agree, it could be great to have this instead of copy-pasting everything all the time.

[fpottier]

On a related note, it would be nice if a grader could access certain common OCaml libraries (perhaps taken from a fixed set; or, ideally, declared by the grader itself). I am thinking for instance of pprint, but I am sure many others would be useful.

[fpottier]

Another library that I would like to use is Seq, which is standard in OCaml 4.07 and is emulated by an opam package in earlier versions. It is useful to program exhaustive enumerations of test cases.