Properly expose github-jsoo and add missing dependencies

[rgrinberg]

Everything but the rename looks good. Shouldn't the module be Github_jsoo?

[samoht]

@rgrinberg I am trying to reflect what we do in github-lwt: I guess it's yet an other instance of the linking trick: github.mli is generated by the core lib and lwt as well as jsoo are implementing it for different backends.

[rgrinberg]

I see. So I guess this will need variants support to fully work.

[avsm]

varianttsssssssssssss