Update details for `ForAllTy` and `ForAllCo` in core-spec, as they
can now quantify over coercion variables.
This patch also renamed core-spec.mng to core-spec.ott as I found it more
natural to edit on .tex file and let ott generate the .mng file,
so that while editing I get full tex-mode support from my editor.
If there is some reason I am missing for using .mng file please let me know
and I am happy to revert the change as well.