Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 ceval(Arg1)

 cquery(Arg1)

 cmod(Arg1)

 crun(Arg1)

 cstart

 creq(Arg1, Arg2)

 get_(Arg1, Arg2, Arg3)

 set_(Arg1, Arg2, Arg3, Arg4)