Mdx_top.init can be parameterized by dirs, packages and predicates

[gpetiot]

@NathanReb let me know if this is what you had in mind, before I go further (if yes, I still have to re-architecture the lib to make the whole test function customizable by the dirs).

[NathanReb]

I think the most important part here the ~dirs argument as that's the only thing dune will need to provide since the libraries will already be linked in.

I think it makes sense to expose packages and predicates as arguments as well.
Obviously once we've extracted the test logic into a library, they should be arguments, of the entry point for running the tests.

[gpetiot]

I defined a new library mdx.test, let me know if that's enough for dune.

[gpetiot]

I rebased it on master, @voodoos if there is everything you need for the mdx stanza for dune I think we should merge this one, as it's a bit painful to rebase when there is any change in bin/test/main.ml (which happens often)

[voodoos]

I think everything I need is here, as Nathan said, it is mostly the ~dir parameter which will be useful.

@NathanReb, do you see anything missing ?

[NathanReb]

Sure you're right, let's merge this, we can always make changes later if it needs some adjustment. It is already a good change on its own to move the logic from the bin/test/main.ml to the library.

Thanks for working on this and sorry the rebase hassle!