Static deployment of learn-ocaml

[erikmd]

Following our latest discussion with @yurug and @leunam217, it seems learn-ocaml is no more deployable statically, i.e., without the ocaml server runtime.

This static-deployment feature could be interesting to allow people put their compiled exercises in a private GitHub repo, and automatically expose the exercises using GitHub Pages (which could just as well be graded at client slide, except that the Sync feature would not be available).

Even if this is not high-priority, it may be worth it to have this feature.

[erikmd]

FIxed by #356