allow different functions to recurse on the same type, like in the old package

improved 'datatype_new_compat': generate more fixpoint equations for types like 'datatype_new x = C (x list) (x list)' (here, one equation for each x list instead of a single for both), for higher compatibility + code generation attributes on the recursor

made N2M more robust w.r.t. identical nested types

register bnfs for (co)datatypes under their proper name (lost in af71b753c459)

updated keywords;

restored old 'remotify' logic -- too many bugs were introduced when refactoring the code

more (co)datatype docs